1 6.0 DREDGING AND EXCAVATION 

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3 TABLE OF CONTENTS

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5 6.0 DREDGING AND EXCAVATION ................................................ 6-1

6 6.1 INTRODUCTION ....................................................... 6-1

7 6.2 ADVANTAGES AND DISADVANTAGES .................................. 6-2

8 6.3 EXCAVATION TECHNOLOGIES ......................................... 6-4

9 6.4 DREDGING TECHNOLOGIES ............................................ 6-5

10 6.4.1 Mechanical Dredging ............................................. 6-5

11 6.4.2 Hydraulic Dredging .............................................. 6-7

12 6.4.3 Dredge Equipment Selection ....................................... 6-8

13 6.4.4 Dredge Positioning .............................................. 6-10

14 6.4.5 Control of Dredging Losses and Residuals ........................... 6-14

15 6.4.6 Containment Barriers ............................................ 6-15

16 6.5 TRANSPORTATION AND STORAGE .................................... 6-18

17 6.6 TREATMENT ......................................................... 6-19

18 6.6.1 Pre-Treatment ................................................. 6-20

19 6.6.2 Operational Treatment ........................................... 6-20

20 6.7 DISPOSAL ........................................................... 6-27

21 6.7.1 Sanitary/Hazardous Waste Landfills ................................ 6-28

22 6.7.2 Confined Disposal Facilities ...................................... 6-29

23 6.7.3 Contained Aquatic Disposal ...................................... 6-30

24 6.7.4 Losses From Disposal Facilities ................................... 6-30

25 6.7.5 Beneficial Use ................................................. 6-30

26 6.8 SITE CONSIDERATIONS ............................................... 6-31

27 6.8.1 Physical Environment ........................................... 6-31

28 6.8.2 Sediment Characteristics ......................................... 6-32

29 6.8.3 Waterway Uses and Infrastructures ................................. 6-32

30 6.8.4 Habitat Alteration ............................................... 6-34

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32 HIGHLIGHTS

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34 Highlight 6-1: Example Flow Diagram for Dredging/Excavation .............................. 6-1

35 Highlight 6-2: Excavation Following Isolation Using Sheet Piling ............................. 6-5

36 Highlight 6-3: Permanent or Temporary Rerouting of the Waterbody .......................... 6-6

37 Highlight 6-4: Examples of Mechanical Dredges .......................................... 6-7

38 Highlight 6-5: Examples of Hydraulic Dredges ............................................ 6-9

39 Highlight 6-6: Operational Characteristics of Various Dredges .............................. 6-11

40 Highlight 6-7: Selection of Dredges for Contaminated Sediment Removal ..................... 6-12

41 Highlight 6-8: Typical Configuration of Silt Curtains and Screens ............................ 6-17

42 Highlight 6-9: Example of Dredging Dewatering Process ................................... 6-20

43 Highlight 6-10: Sediment Treatment Examples ........................................... 6-22

44 Highlight 6-11: NY/NJ Harbor - Treatment Technologies and Beneficial Use ................... 6-27

45 Highlight 6-12: Summary of Disposal Technologies ....................................... 6-28

46 Highlight 6-13: Cross Section of a Confined Disposal Facility Dike with a Filter Layer ........... 6-29

47 Highlight 6-14: Dredging/Disposal Feasibility Tests ...................................... 6-33

48 Highlight 6-15: Points to Remember When Considering Dredging and Excavation............... 6-35
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Chapter 6: Dredging and Excavation 

6.0 DREDGING AND EXCAVATION 

6.1 INTRODUCTION 

Dredging and excavation are means of removing contaminated sediment from a waterbody, either 

while it is submerged (dredging) or after water has been diverted or drained (excavation). Both methods 

necessitate transporting the sediment to a location for treatment and/or disposal of the sediment. They 

also frequently need treatment of water from dewatered sediment prior to discharge. Sediment is dredged 

on a routine basis at numerous locations for the maintenance of navigation channels. Use of the term 

environmental dredging has evolved in recent years to characterize dredging performed specifically for 

the removal of contaminated sediment. The objective of navigational dredging is to remove sediment as 

efficiently and economically as possible to maintain waterways for recreational, national defense, and 

commercial purposes. Environmental dredging is intended to remove sediment contaminated above 

certain action levels while minimizing the spread of contaminants to the surrounding environment (NRC 

1997). 

The components to be evaluated when considering dredging or excavation as a cleanup method 

are removal, transport and storage, treatment (pretreatment, treatment of decant and/or dewatering 

effluents and sediment, if necessary), and disposal (liquids and solids). Highlight 6-1 provides a flow 

diagram of the steps in a typical dredging or excavation alternative. In its simplest form, a dredging or 

excavation project may consist of as few as three of the components shown in Highlight 6-1. A complex 

project may include all of these components. 

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Removal Transport Storage Pretreatment Treatm ent 

Air or Gas Residue 

Treatment 

W ater Effluent 

Treatment and/or 

Disposal 

Disposal and/or 

Reuse 

Disposal and/or 

Reuse 

Solids 

Contaminated 

Solids 

Solids 

Highlight 6-1: Example Flow Diagram for Dredging/Excavation 

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Sediment removal by dredging or excavation is the most frequent cleanup method for sediment 

used by the Superfund program in the past. Dredging or excavation have been selected as a cleanup 

method for contaminated sediment at more than 100 Superfund sites as of 2001 (some as an initial 

removal action). At about 15 to 20 percent of these sites, an in-situ method was also selected for 

sediment at part of the site. In general, project managers should evaluate each of the three cleanup 

methods: monitored natural recovery, in-situ capping, and removal through dredging or excavation, at 

every sediment site at which they may be appropriate. 

Project managers should also refer to the U.S. Environmental Protection Agency’s Assessment 

and Remediation of Contaminated Sediments (ARCS) Program Remediation Guidance Document (U.S. 

EPA 1994b) and Handbook:Remediation of Contaminated Sediments (U.S. EPA 1991b), and the National 

Research Council’s (NRC’s) Contaminated Sediments in Ports and Waterways: Cleanup Strategies and 

Technologies (NRC 1997) for detailed discussions of the processes and technologies available for 

dredging and excavation. The project manager should evaluate the entire removal process with a 

coordinated systems approach. Efficient coordination of each component is important for a cost-effective 

cleanup. 

6.2 ADVANTAGES AND DISADVANTAGES 

One of the principal advantages of removing contaminated sediment from the aquatic 

environment is that , where it is done effectively, sediment removal may result in the least uncertainty 

about long-term effectiveness of the cleanup, particularly regarding future environmental exposure to 

contaminated sediment. Removal of contaminated sediment can minimize the uncertainty associated with 

predictions of sediment bed or in-situ cap stability and the potential for exposure and transport of 

contaminants. 

Another principal advantage of removal of contaminated sediment is the flexibility it leaves 

regarding future use of the waterbody. In-situ cleanup methods such as monitored natural recovery and 

capping frequently need institutional controls which limit waterbody uses. Sediment removal usually 

requires fewer institutional controls because larger amounts of contaminants do not remain in place in the 

aquatic environment. 

Another advantage, where dredging residuals are low, concerns the time to achieve remedial 

action objectives. Active cleanup methods such as sediment removal and capping may reduce risk more 

quickly by achieving faster reductions in sediment concentrations. Contaminant uptake can be limited or 

controlled by disposing the dredged or excavated material in an alternate setting, such as an engineered 

landfill, upland or nearshore confined disposal facility (CDF), or contained aquatic disposal (CAD). 

Also, sediment removal is the only cleanup method which allows for treatment and/or beneficial reuse of 

dredged or excavated material. Treatment of contaminated sediment can also reduce the demands on 

limited landfill disposal capacity. 

There are also significant disadvantages to sediment removal. Implementation of dredging or 

excavation is usually more complex and costly than monitored natural recovery or in-situ capping 

because of the removal technologies themselves (especially in the case of dredging) and the need for 

transport, storage, treatment (where applicable), and disposal. Treatment technologies for contaminated 

sediment offer implementation challenges because of limited full-scale experience and cost. Disposal 

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Chapter 6: Dredging and Excavation 

capacity may be limited in existing municipal or hazardous waste landfills and it may be difficult to site 

new local disposal facilities. 

Another disadvantage of sediment removal is the residual contamination left following removal, 

especially when dredging is used. No removal technology can remove every particle of contaminated 

sediment, and especially where work is conducted under water, there can be significant uncertainties 

concerning the extent of residuals. Residual contamination is likely to be greater in the presence of 

cobbles, boulders, or buried debris, in high energy environments, at greater water depths, and where 

contaminated sediment directly overlies bedrock or a hard bottom. These complicating factors can make 

the sediment removal process and achievement of remediation goals difficult and costly. 

Another disadvantage of dredging includes the increased potential for contaminant losses through 

resuspension and, generally, to a lesser extent through volatilization. Resuspension of sediment from 

dredging will result in both dissolved and particle-associated releases to the water column. Resuspended 

particulate material may be redeposited at the dredging site or, if not controlled, transported to other 

locations in the waterbody downstream. Some resuspended contaminants may also dissolve into the 

water column where they are available for uptake by biota. While aqueous resuspension is much less of a 

concern during excavation, there may be increased concern with releases to air. Losses at the disposal or 

treatment site may include effluent or runoff discharges to surface water, leachate discharges to ground 

water, or volatile emission to air. Each component of a sediment removal alternative necessitates 

additional handling of the material and presents a possibility of contaminant loss. 

Finally, short-term disruption of the benthic environment is unavoidable during dredging or 

excavation and includes at least a temporary destruction of the aquatic community and habitat within the 

remediation area. If removed sediment is to be disposed of in an in-water disposal site, there may be 

additional impacts to sensitive ecological environments in or near the in-water disposal site. 

Where it is feasible, excavation sometimes has advantages over dredging for the following 

reasons: 

• It is difficult to visually observe the removal operation underwater. Although in some 

cases diver-assisted hydraulic dredging or video-monitored dredging can be used to guide 

the removal operation, turbidity, safety and other constraints typically make it necessary 

for dredging to be performed without visual assistance; 

• Water flow in the dredged area during removal may result in greater potential for 

waterborne releases; and 

• Water bottom conditions (e.g., debris) and sediment characteristics (e.g., grain size and 

specific gravity) typically require greater consideration than for excavation. 

However, site preparation for excavation can be more lengthy and costly than for a dredging project due 

to the need for dewatering or water diversion. 

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Chapter 6: Dredging and Excavation 

6.3 EXCAVATION TECHNOLOGIES 

Excavation of contaminated sediment generally involves isolating the contaminated sediment 

from the overlying waterbody, pumping or diverting water from the area, and managing any continuing 

inflow followed by sediment excavation using conventional dryland equipment. However, excavation 

may be possible without water diversion in some areas such as wetlands during dry seasons or while the 

sediment and water are frozen. Typically, excavation is performed in shallow waterbodies or near shore 

areas. 

Prior to pumping out the water, the area is isolated using the following: 

• Sheet piling; 

• Earthen dams; 

• Rerouting the waterbody using temporary dams or pipes; or 

• Permanent relocation of the waterbody. 

Sediment isolation using sheet piling commonly involves driving interlocking metal plates (sheet 

piles) into the subsurface, and thereby either blocking off designated areas or splitting a stream down the 

center. Highlight 6-2 shows an example of where this has been used. Sheet piling may not be feasible 

where bedrock or hard strata are present at or near the surface. If a stream is split down its center, then 

one side of the stream may be excavated in the dry. When the excavation of the first side of the stream is 

completed, water may be diverted back to the excavated side and sediment on the other side may be 

excavated. Temporarily rerouting a waterbody with dams is sometimes done for small streams or ponds 

(Highlight 6-3). This includes the use of temporary dams to divert the water flow allowing excavation of 

contaminated sediment. The ability and cost to provide hydraulic isolation of the contaminated area 

during remediation is a major factor in selecting the appropriate removal technology. 

Once isolated, standing water within the excavation area will need to be removed. As surface 

water flows are eliminated ground water may infiltrate the confined area. The ground water can be 

collected in sumps or dewatering wells. After collection, the ground water should be characterized, 

managed, treated (if necessary), and discharged to an appropriate receiving waterbody. Management of 

water within the confined area is an important logistical and cost factor that can influence the decision of 

wet versus dry removal techniques. 

Isolation and dewatering of the area is normally followed by excavation using conventional 

earthmoving equipment such as a backhoe or dragline. When the excavation activities are complete, 

temporary dam(s) or sheet piling(s) are removed and the waterbody is restored to its original hydraulic 

condition. The stream bank and bed may need to be restabilized or restored upon completion of the 

remediation project depending on applicable regulations. 

Another less common type of excavation project involves permanent relocation of a waterbody 

(Highlight 6-3). The initial phases of such a project may be similar to excavation projects that 

temporarily reroute a waterbody. However, in a permanent stream relocation project, a replacement 

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Chapter 6: Dredging and Excavation 

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Highlight 6-2: Excavation Following Isolation Using Sheet Piling 

Source: Pine River/Velsicol, EPA Region 5 

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6 stream is constructed before the original waterbody is capped and converted into an upland area. Because

7 the original waterbody is covered over, direct exposure to residual contamination is reduced or

8 eliminated.

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10 Excavation may also include excavation of sediment in areas that experience occasional dry

11 conditions, such as intermittent streams and wetlands. These types of projects are logistically similar to

12 upland construction projects and frequently use conventional earthmoving equipment.

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14 6.4 DREDGING TECHNOLOGIES

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16 Dredging projects are conducted underwater. Dredging involves mechanically penetrating,

17 grabbing, raking, cutting, or hydraulically scouring the bottom of a waterway to dislodge the sediment.

18 Once dislodged, the sediment may be removed from a waterway either mechanically(with buckets) or

19 hydraulically (by pumping). Therefore, dredges may be categorized as either mechanical or hydraulic

20 depending on the basic means of moving the dredged material. Some dredges employ pneumatic

21 (compressed air) systems to pump the sediment out of the waterway (U.S. EPA 1994b).

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23 6.4.1 Mechanical Dredging

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25 The fundamental difference between mechanical and hydraulic dredging equipment is the form in

26 which the sediment is removed. Mechanical dredges offer the advantage of removing the sediment at

27 nearly the same solids content and, therefore, volume as the in-situ material. Little additional water is 

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Chapter 6: Dredging and Excavation 

Highlight 6-3: Permanent or Temporary Rerouting of the Waterbody 

A: Permanent River Relocation – Triana/Tennessee River Site 

The Triana/Tennessee River Site consists of an 11-mile stretch of two tributaries, the Huntsville Spring Branch and 

Indian Creek, which both empty into the Tennessee River. involved rerouting of the channel in 

Huntsville Spring Branch (HSB mile 5.4 to 4.0), the filling and burial in place of the DDTR (dichloro diphenyl 

trichloroethane and its metabolites) in the old channel, the construction of diversion structures at the upper and 

lower end of the stream to prevent stream reversion to the former stream channel, and the diversion of storm water 

runoff to prevent flow across the filled channel. tions for HSB mile 4.0 to 2.4 consisted of constructing 

four diversion structures; excavating a new channel between HSB mile 3.4 and 2.4; filling three areas; constructing 

a diversion ditch around the fill areas; and excavating portions of the sediment from the channel. 

These remedial actions effectively isolated in place 93% of the DDTR in the Huntsville Spring Branch-Indian Creek 

system of the Tennessee River. hese remedial actions began on April 1, 1986, and were completed on October 

16, 1987. hrough March 1, 2001, the remedial actions have been inspected yearly by a federal and state Review 

Panel. he remedial action has not required any repair of the structures to maintain their integrity, and monitoring 

has shown that DDTR concentrations in fish and water continue to decline. 

B: Temporary Re-Routing of a River – Bryant Mill Pond Project at the Allied Paper, Inc./Portage 

Creek/Kalamazoo River Site 

In EPA Region 5, an EPA-conducted 

removal and onsite containment 

action removed polychlorinated 

biphenyls (PCBs)-contaminated 

sediments from the Bryant Mill Pond 

area of Portage Creek. 

removal action, that was conducted 

from June 1998 - May 1999, Portage 

Creek was temporarily diverted from 

its normal streambed so that 150,000 

cu yds of the creek bed and 

floodplain soils could be excavated 

using conventional excavation 

equipment. 

remaining after the removal action 

were below 1 ppm. 

Source: U.S. EPA Region 5 

Remedial actions 

Remedial ac

T

T

T

During the 

PCB concentrations 

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25 entrained with the sediment as it is removed. Thus, the volumes of contaminated material and process

26 water to be disposed, managed, and/or treated are minimized. Major types of mechanical dredges that

27 have been used in environmental dredging include clamshell bucket (including specialized enclosed

28 clamshell buckets) and backhoes. 

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30 Redesigned environmental clamshell dredges address a number of issues often raised relative to

31 remedial dredging including contaminant removal efficiency, sediment resuspension, and overall cost. A

32 new technology tested at the New Bedford Harbor Superfund site in Massachusetts involved precise

33 positioning of the dredging apparatus to minimize over-dredging, a sealed horizontal profiling clamshell

34 bucket to minimize resuspension, and a water recirculating system that reduces water treatment for the

35 hydraulic dredge material pipeline system. Results indicate that PCB-contaminated sediment removal

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Chapter 6: Dredging and Excavation 

1 efficiency was very high (> 97 percent) and that resuspension due to dredging was almost non-detectable. 

2 Highlight 6-4 shows two examples of mechanical dredges including the type used at New Bedford. 

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5 Highlight 6-4: Examples of Mechanical Dredges 

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9 Note: A = Use of specially designed “environmental” mechanical dredges cam reduce suspension (Source: Cable Arm, Corp.) 

B = New Bedford Site; Bean Company prototype low-resuspension mechanical dredge (Source: Barbara Bergen, U.S. EPA) 

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11 6.4.2 Hydraulic Dredging

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13 Hydraulic dredges remove and transport sediment in the form of a slurry through the addition of

14 high volumes of water at some point in the removal process (Zappi and Hayes 1991). The total volume of

15 material processed may be greatly increased and the solids content of the slurry may be considerably less

16 than that of the in-situ sediment although solids content varies between dredges (U.S. EPA 1994b). The

17 excess water is usually discharged as effluent at the treatment or disposal site and may need treatment

18 prior to discharge. Hydraulic dredges may be equipped with rotating blades, augers, or high-pressure

19 water jets to loosen the sediment (U.S. EPA 1995b). The ARCS Remediation Guidance 

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Chapter 6: Dredging and Excavation 

Document (U.S. EPA 1994b) contains figures and summaries of dredge capabilities for several commonly 

available hydraulic dredges. The hydraulic dredges most commonly used in the U.S. are the conventional 

cutterhead dredge and the horizontal auger. 

Certain hydraulic dredges such as the modified dustpan dredge, cleanup dredge, horizontal 

profiling grab dredge, Eddy pump, and matchbox dredges, have been specifically developed to reduce 

resuspension during the removal process. Redesigned hydraulic dredges have recently been tested that 

can move sediment with less water and others that recycle the water used to move the sediment. Highlight 

6-5 presents examples of hydraulic dredges. 

6.4.3 Dredge Equipment Selection 

The selection of appropriate dredging equipment is essential for an effective dredging operation. 

The following factors should be evaluated: 

• Solids Concentration: In most cases it is preferable to use a dredging system that is 

capable of delivering material at high solids concentrations to minimize costs for 

handling, treating, and disposal of water and sediment. However, in some cases the 

advantages of slurried sediment that may be transported by pipeline may override these 

considerations; 

• Production Rate: A high production rate or large dredge may be necessary to complete 

large projects within acceptable time frames or necessary to cut through harder sediment. 

Alternatively, a low production rate may be beneficial to minimize sediment resuspension 

or because of constraints caused by sediment transport, treatment, or disposal 

components, or when rocks or debris are present in the sediment; 

• Dredging Accuracy: Precise control of operational dredging depth is particularly 

important when dredged sediment is to be handled in expensive treatment and disposal 

facilities (Averett et al. 1990). The vertical and lateral accuracy of the dredge is 

important to ensure that contaminated sediment is removed, while minimizing the amount 

of clean sediment removed; 

• Water 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 sediment is located outside of navigable waterways. Some dredging 

equipment may be operated from land to access sediment in shallow waterways. The 

maximum depth to which dredges reach may be a limiting factor. Some dredges are 

limited by the length of the dredging arm or ladder. Hydraulic dredging in very deep 

water (i.e., greater than 20 meters) may need submerged pumps or remotely operated 

dredges; 

• Ability to Handle Large or Dangerous Debris: Sediment, especially in urban areas and 

cargo loading/unloading areas may contain very large debris (e.g., greater than 0.5 meters 

in any dimension) which can only be removed mechanically. Mechanical dredges 

generally remove large debris with the sediment, however they may produce greater 

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Chapter 6: Dredging and Excavation 

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Highlight 6-5: Examples of Hydraulic Dredges 

Note: A = Fox River, WI; horizontal auger hydraulic dredge deployment (Source of photo, Jim Hahnenberg U.S. EPA) 

B = Manistique, MI; closeup of twin-vortex pump, hydraulic dredge cutterhead (Source of photo, Ernie Watkins U.S. EPA) 

C = Closeup of swinging ladder hydraulic dredge cutterhead (Source of photo, Ellicott Corporation) 

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8 turbidity in the process. Dredgeheads equipped with cutters may be able to reduce the 

9 size of some debris, such as wood. Although debris that is larger than the diameter of the 

10 suction pipe or not cut by the cutter cannot be removed by hydraulic dredges, smaller 

11 debris may also clog hydraulic pipelines and damage pumps. At some sites the risk and 

12 approach for dealing with buried munitions from past military activities should be 

13 evaluated; 

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15 • Sediment Resuspension, Release and Residual Concentration: Sediment resuspension, 

16 contaminant release, and residual sediment concentrations are primary concerns at many 

17 sites and may override other factors in selecting a dredge. The degree of resuspension is 

18 influenced by both the type of dredge and its operation. Specialty dredges have been 

19 designed in recent years to minimize resuspension, although dredge operation is 

20 extremely important; 

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22 • Site Restrictions: Channel widths, surface and submerged obstructions, overhead 

23 restrictions, such as bridges, and other site access restrictions may limit the type and size 

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of equipment that can be used. The presence of buried utilities, pipelines, and other 

infrastructure should also be considered in the evaluation of dredging technologies; 

• Compatibility: The overall compatibility of dredging equipment with the transport, 

treatment, and disposal requirements for the project is critical to an efficient and effective 

dredging remedy. 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 sediment. Mechanically dredged sediment does not 

need intensive dewatering, which is an expensive pre-treatment process. Mechanical 

dredging keeps the volume of dredged material to a minimum and greatly reduces the 

costs of water treatment; and 

• Distance to Treatment or Disposal Sites: The distance from the dredging site to the 

treatment, disposal, or re-handling site affects the method of transport and, hence, the 

type of dredge. If there is access for a pipeline slurried sediment can be transported by 

pipeline several kilometers where there is little elevation gain, and can be transported 

over longer distances with the use of booster pumps. If pipeline transport is not feasible, 

sediment can be transported at high solids concentrations (e.g., as produced with 

mechanical or pneumatic dredges) by scows or barges, provided that the water is deep 

enough for barge transport and there are no other limitations on navigation. 

The operational characteristics of conventional mechanical and hydraulic dredges are shown in 

Highlight 6-6. Highlight 6-7 displays an assessment of various dredges against the factors listed above 

and additional factors that may be important in dredge selection at some sites. The information in these 

highlights is intended as general guidelines to help project managers make an initial assessment of dredge 

capabilities. There are many site specific circumstances that dictate which equipment will work for any 

given situation. In addition, because new equipment is being continuously developed, project managers 

will need to consult with experts who are familiar with the latest technologies in order to make a final 

selection. 

Experience has shown that an environmentally effective dredging operation depends on the use of 

highly skilled dredge operators familiar with the goals of environmental remediation, in addition to close 

monitoring and management of the dredging operation. For additional advice regarding dredge 

equipment selection and use project managers should consult professionals in this field and the additional 

technical documents listed in Appendix D. 

6.4.4 Dredge Positioning 

A critical element of sediment remediation is the precision of the dredge cut, both horizontally 

and vertically. Technological developments in surveying (vessel) and positioning (dredgehead) 

instruments have improved the dredging process. Vertical control may be particularly important when 

contamination occurs in a relatively thin or uneven layer. Video cameras may be used to continuously 

monitor dredging operations. The working depth of the dredgehead may be measured using acoustic 

instrumentation and by monitoring dredged slurry densities. In addition, surveying software packages 

may be used to generate pre- and post-dredging bathymetric charts, determine the volume of dredged 

sediment, locate obstacles, and calculate linear dimensions of surface areas (St. Lawrence Centre 1993). 

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Chapter 6: Dredging and Excavation 

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1516171819202122 

Highlight 6-6: Operational Characteristics of Various Dredges 

Dredge Type1 

Percent Solids 

by Weight 

Range of Production Rates 

(cubic m/hr)2 

Dredging Accuracy3 Operational Dredging Dept

Vertical (cm) Horizontal (m) Minimum (m) 

4 Maximum (

Clamshell or Grab Near in-situ 20-500 10-60 0.1-0.3 50 

Backhoe Near in-situ 20-150 5-30 0.05-0.15 15 

Enclosed Bucket Near in-situ 20-500 5-30 0.1-0.3 50 

Bucket/pump Near in-situ 20-150 5-30 0.05-0.15 15 

Cutterhead (6-8 in.) 10-20 20-100 5-30 0.1-0.5 1.2 4 

Cutterhead (10-12 in.) 10-20 60-500 5-30 0.1-0.5 1.4 8 

Cutterhead (14-18 in.) 10-20 200-900 5-30 0.1-0.5 1.5 12 

Horizontal Auger (6-18 in.) 10-30 50-100 5-15 0.15-0.5 0.5 5 

Pneumatic 25-40 50-300 5-30 0.1-0.3 45 

Diver Assisted Vacuum 5-10 10 0.15 0.5 30 

Plain Suction 5-15 20-4000 5-30 0.1-0.5 2 19 Dry Excavation In situ or greater 10-500 10 0.1 0 Stability 

Limitations 

1 This table only includes dredge sizes normally considered for environmental projects. Larger dredge sizes commonly used for navigation dredging are available. 2 Production rates include both environmental and navigational dredging. Removal of contaminated sediments tend toward the low end of the range.3 Where a range is shown for positioning accuracy, the lower value reflects use of state-of-the-art electronic positioning equipment to define dredgehead position employed und

while the upper value reflects use of electronic positioning for the vessel only with visual indicators of dredgehead positioning with respect to the vessel. 

4 Note that the minimum operating depth limitations may be overcome by an excavation sequence from deeper water into the area to be dredged. 

Sources: U.S. EPA 1994b, USACE 1983, Bray 1997, Herbich 1992 

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10 11 12 13 14 
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2 3 4 5 6 7 8 9 

10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 

Highlight 6-7: Selection of Dredges for Contaminated Sediment Removal 

Dredging Issue/ Concern/ Constraint 

Mechanical Dredges Hydraulic Dredges 

Clamshell Backhoe 

Enclosed 

Bucket 

Bucket/ 

Pump Cutterhead 

Horizontal 

Auger Pneumatic 

DiverAssisted 

Vacuum 

Sediment resuspension1 , [ [ [ 0 [ 

Volatiles control , , [ [ [ [ Low clean-up targets , , , , [ [ Spillage , , [ [ [ [ Transport by pipeline , , [ [ [ [ Transport by barge [ [ [ , , High solids concentration [ [ , , , , Vertical cut control , , , [ [ , , Lateral cut control , , [ , [ , , Positioning support required 0 0 [ 0 Shallow water (<3 ft) , [ [ [ , [ Deep water (>20 ft) [ 0 , , Current/tides2 [ [ [ , , 

Piers and utilities [ [ [ , , [ 

Debris/boulders/rocks3 [ [ , , , , , Vegetation removal4 [ [ , , , , Production rate [ , [ [ , , Hardpan (native clay/till) [ [ , , [ , Thin lift for removal , , , , [ [ Availability [ [ [ Portability , [ [ [ , [ 

Positioning control , [ [ , [ , 

, [ 

[ [[ [ [ [ 

, ,

, , ,

[ [[ [ 

0 0 [ 0 

, ,

[ [ 0 [

, , ,, ,

[ 

[ [[ [

, ,

[ [ 

[ [ [ [ [ 

, ,

[ [ 

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1 23456789

101112 

Dredging Issue/ Concern/ Constraint 

Mechanical Dredges Hydraulic Dredges 

Clamshell Backhoe 

Enclosed 

Bucket 

Bucket/ 

Pump Cutterhead 

Horizontal 

Auger Pneumatic 

DiverAssisted 

Vacuum 

Operator health & safety , , , [ [ Note: [ indicates a technology which may generally be favorable for addressing this issue or concern , indicates a technology which may not be generally favorable for addressing this issue or concern 

0 es a technology which may be neutral for addressing this issue or concern 

1 Conventional backhoes are normally used for dry excavation and can cause resuspension when used in wet environments. Special enclosed backhoes can be used if resus2 Most mechanical dredges are able to maintain their position in currents and tides better than hydraulic dredges.3 In general mechanical dredges have advantages in removing debris and boulders, although they may have trouble closing because of these obstructions, resulting in leakag

Hydraulic dredges can pass moderate sized rocks and can suction around boulders. 

4 Many hydraulic dredges have problems removing vegetation without becoming clogged. 

[ [ [

indicat

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Digital positioning systems are available that enable dredge operators to follow a complex sediment 

contour (Van Oostrum 1992). 

The horizontal position of the dredge should be continuously monitored during dredging. 

Satellite- or transmitter-based positioning systems, such as differential global positioning systems (DGPS) 

should be used to define the dredge position. In some cases, however, the accuracy of these systems is 

inadequate for precise dredging control. Where the accuracy of site characterization data or the high cost 

of disposal warrant very precise control, it is possible to use optical (laser) surveying instruments set up at 

one or more locations on shore. These techniques, in conjunction with on-vessel instruments and spuds 

(if water depths are less than about 50 feet) and anchoring systems may enable the dredge operator to 

more accurately target specific sediment deposits. The effectiveness of anchoring systems diminishes as 

water depth increases. 

The positioning technology described above enhances the accuracy of dredging. However, 

project managers should not develop unrealistic expectations of dredging accuracy. Contaminated 

sediment may not be removed with surgical accuracy even with the most sophisticated equipment. 

Equipment may not be the only factor affecting the accuracy of the dredging operation. Site conditions 

(e.g., weather, currents), sediment conditions (e.g., bathymetry, physical characteristics), and the skill of 

the dredge operator are all important factors. In addition, the distribution of sediment contaminants may 

only be defined at a crude level and there could be a substantial margin for error. The level of accuracy 

required for environmental dredging should reflect the accuracy needed to attain the remedial action 

objectives. 

6.4.5 Control of Dredging Losses and Residuals 

In environments with significant water movement due to tides or currents, resuspended sediment 

may be transported away from a dredging site; therefore, limiting resuspension or increasing containment 

should be an important consideration. Another potential problem may be the volatilization of 

contaminants that reach the water’s surface, either near the dredge site or in a holding facility (Chiarenzeli 

et al. 1998). 

When evaluating short-term effects of dredging, it is important to compare impacts to baseline 

conditions including water quality impacts due to any natural sediment disruption that would continue to 

occur if the contaminated sediment was not dredged. All dredges resuspend some sediment during the 

dredging processes. Some contaminants in the dissolved form and some contaminants associated with 

resuspended particles will be released and transported away from the dredging site. Monitoring during 

dredging is critical to evaluate resuspension and its effects on water quality. Much can be done to limit 

sediment resuspension from conventional dredges without substantial impact upon the efficiency of the 

dredging operation. Precautions in operation and/or minor plant modifications can be made with only a 

small increase in cost, however, other factors such as maneuverability requirements, hydrodynamic 

conditions, and location of the disposal site may dictate the type of dredge that should be used. The 

strategy for the project manager should be to minimize the resuspension levels generated by any specific 

dredge type. If conventional dredges are unacceptable, a special purpose dredge may be required. These 

dredges generally resuspend less material than conventional dredges, but associated costs may be much 

greater. As in the case of conventional dredges, the selection of a special purpose dredge will likely be 

dictated by site specific conditions, economics, and availability (Palermo et al. 1998b). The EPA’s Office 

of Research and Development and others are in the process of evaluating resuspension and its effects, 

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both in field and modeling studies. The results of this research should help project managers predict and 

control effects of resuspension during future cleanup actions. 

During dredging volatile contaminants trapped in the sediment may be released to the water 

column and atmosphere in the vicinity of the dredge and/or at the CDF posing a potential risk to workers 

and the nearby community. This exposure route may be minimized by reducing dredging production 

rates so that resuspension is minimalized. Covering the surface of the water with a physical barrier or an 

absorbent compound may minimize volatilization. At the New Bedford Harbor site, a cutterhead dredge 

was modified by placing a cover over the dredgehead that retained PCB-laden oils, thus reducing the air 

concentrations during dredging to background levels (Bergen in preparation). In addition, the CDF that 

the dredged sediment was pumped into was fitted with a plastic cover to effectively reduce air emissions. 

To further minimize the potential for volatile releases, dredging operations were conducted during cooler 

weather periods, such as at night. 

During excavation, volatilization could be of greater concern as contaminated materials may be 

exposed to air. Care should be taken in dewatering activities to ensure that temperatures are not elevated 

(e.g., cautious application of lime or cement for de-watering), and other control measure should be taken 

as needed (e.g., foam). 

The potential for residual contamination left behind by the dredging operation is dependent on a 

number of factors including the design and operating mode of the dredgehead, the size of the dredge (e.g. 

cutterhead diameter), operating parameters (e.g. swing speed, advance rate of the dredge, cutter rotation, 

and depth of burial of the dredgehead), skill of the operator, sediment physical properties, thickness of the 

layer to be removed, and site hydrodynamics such as currents and waves. Additional passes of the dredge 

may be required to achieve the desired results. Placement of a thin layer of clean material designed to 

mix with underlying sediment is another approach to address the problem of residual sediment. Project 

managers should conduct a site-specific assessment of anticipated sediment resuspension, contaminant 

release and transport, and its potential ecological impacts prior to dredging. Also, the project manager 

should make realistic assumptions regarding residual contamination. Where over dredging is not 

possible, residual contamination is generally higher than where this practice is possible. 

6.4.6 Containment Barriers 

Transport of resuspended contaminated sediment released during dredging can often be reduced 

by using physical barriers around the dredging operation. Barriers commonly used to reduce the spread 

of contaminants during the removal process include oil booms, silt curtains, silt screens, sheet-pile walls, 

and cofferdams (U.S. EPA 1994b). Under favorable site conditions these barriers help limit the areal 

extent of particle bound contaminant migration resulting from dredging resuspension and enhance the 

long-term benefits gained by the removal process. Conversely, because the barriers contain resuspended 

sediment they typically increase contaminant concentrations inside the barrier where it may need to be 

managed. 

Structural barriers, such as sheet pile walls, have been used for sediment excavation and in some 

cases (e.g., high current velocities) for dredging projects. The determination of whether these types of 

barriers are necessary should be made based on a thorough evaluation of the site. This can be 

accomplished by evaluating the relative risks posed by the anticipated release of contaminants from the 

dredging operation absent use of such structural barriers, the predicted extent and duration of such 

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releases, and the potential for trapping and accumulating residual contaminated sediment within the 

barrier. The project manager should consult the Risk Assessment and Modeling Overview Document 

(U.S. EPA 1993d) and Estimating Contaminant Losses from Components of Remediation Alternatives for 

Contaminated Sediment (U.S. EPA 1996f) for further information about evaluating the need for structural 

barriers. 

Oil booms are appropriate for sediment that may likely release oils or floatables 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, such as polypropylene 

mats (U.S. EPA 1994b). However, booms do not aid in retaining the soluble portion of floatables [e.g., 

polynuclear aromatic hydrocarbons (PAHs) from oils]. 

Silt curtains and silt screens are flexible barriers that hang down from the water surface. 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” may frequently be used interchangeably there are fundamental 

differences. Silt curtains are made of impervious materials, 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 large fraction of 

the suspended solids (Averett et al. 1990). Silt curtains or silt screens may be appropriate when 

contaminant concentrations are high or site conditions dictate the need for minimal transport of 

susupended sediment. A typical configuration of silt curtains or screens is shown in Highlight 6-8. 

Silt curtains have been used at many locations with varying degrees of success. For example, silt 

curtains were found to be effective in limiting suspended solids transport during in-water dike 

construction of the CDF for the New Bedford Harbor pilot project. However, the same silt curtains were 

ineffective in limiting contaminant migration during dredging operations at the same site primarily as a 

result of tidal fluctuation and wind (Averett et al. 1990). Problems were experienced during installation 

of silt curtains at the General Motors site (Massena, New York) due to high current velocities and back 

eddies. Dye tests conducted after installation revealed significant leakage and the silt curtains were 

removed. Sheet piling was then installed around the area to be dredged with silt curtains used as 

supplemental containment for hot spot areas. A silt curtain/silt screen containment system was effectively 

applied during dredging of the Sheboygan River in 1990 and 1991, where water depths were two meters 

or less. A silt curtain was found to reduce suspended solids from approximately 400 milligrams per liter 

(inside) to 5 milligrams per liter (outside) during rock fill and dredging activities in Halifax Harbor, 

Canada (MacKnight 1992). 

The effectiveness of silt curtains and screens at a sediment remediation site is primarily 

determined by the hydrodynamic conditions at the site. Conditions that may reduce the effectiveness of 

barriers include the following: 

• Strong currents; 

• High winds; 

• Changing water levels, such as tidal fluctuation; 

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Chapter 6: Dredging and Excavation 

1 • Excessive wave height, including ship wakes; and

2

3 • Drifting ice and debris.

5 

6 

7

Ma z e 

Ri v e r Current 

U - s h aped , 

in s t r e a m 

Le g e nd 

M o or i n g bu oy 

An c h o r 

S i n g l e an c h or 

o r pi li ng 

U - s hap ed, anc h o r ed ons h o r e 

C i r c ul a r o r el li pt i c a l 

ES T U A R Y 

C urrent 

M o v e m ent s due 

t o re v e rs i n g 

cu r r e n t s 

Highlight 6-8: Typical Configuration of Silt Curtains and Screens 

Source: U.S. EPA 1998d 

9 

10 Silt curtains and screens are generally most effective in relatively shallow, undisturbed water. As 

11 water depth increases and turbulence caused by currents and waves increases, it becomes difficult to 

12 effectively isolate the dredging operation from the ambient water. The St. Lawrence Centre (1993) 

13 advises against the use of silt curtains in water deeper than 6.5 meters or in currents greater than 50 

14 centimeters per second. 

15 

16 The effectiveness of containment barriers is also influenced by the quantity and type of 

17 suspended solids, the mooring method, and the characteristics of the barrier (JBF Scientific Corp. 1978). 

18 To be effective, barriers are deployed around the dredging operation and should remain in place until the 

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operation is completed at that site. For large projects it may be necessary to relocate the barriers as the 

dredge moves to new areas. Where possible barriers should not impede navigation traffic. Containment 

barriers may also be used to protect specific areas, for example valuable habitat, water intakes, or 

recreational areas, from suspended sediment contamination. 

6.5 TRANSPORTATION AND STORAGE 

After removal, sediment is transported to a disposal, storage, or re-handling area for further 

processing or final disposal. Transport links all dredging or excavation components and may involve 

several different technologies or modes of transport. The first element in the transport process is to move 

sediment from the removal site to the disposal, storage, or re-handling site. Sediment may then be 

transported for pretreatment, treatment, and/or ultimate disposal (U.S. EPA 1994b). 

Modes of transportation may include one or more of the following waterborne or overland 

technologies: 

• Pipeline: Direct placement of material into disposal sites by pipeline is economical only 

when the disposal and/or treatment site is located near the dredging areas (typically a few 

kilometers or less unless booster pumps are used). Mechanically dredged material may 

also be re-slurried from barges and pumped into nearshore disposal sites by pipeline; 

• Barge: A re-handling facility located on shore is a commonly considered option. With a 

re-handling facility, dredging can be accomplished with mechanical (bucket) dredges 

where the sediment is excavated at near in-situ density (water content) and placed in a 

scow or barge for transport to the re-handling facility; 

• Conveyor: Conveyors may be used to move material from barges to adjacent re-handling 

facilities or to move material relatively short distances. Materials should be in a 

dewatered condition for transport by conveyor; 

• Railcar: Rail spurs may be constructed to link re-handling/treatment facilities to the rail 

network. Many licensed landfills have rail links, so long-distance transport by rail is 

generally an option; and/or 

• Truck/Trailer: Dredged material can be re-handled directly from the barges to roll-off 

containers or dump trucks for transport to a CDF by direct dumping or unloading into a 

chute or conveyor. Truck transport of treated material to landfills may also be 

considered. The material should be dewatered prior to truck transport over surface streets. 

In some smaller sites where construction of dewatering beds may be difficult or the cost 

of disposal is not great, addition of non-toxic absorbent materials such as lime or cement 

may be feasible. 

A wide variety of transportation methods are available for moving sediment and residual wastes 

with unique physical and chemical attributes. In many cases, contaminated sediment is initially moved 

using waterborne transportation. Exceptions are the use of land-based or dry excavation methods. 

Hydraulic dredges produce contaminated dredged-material slurries that can be transported by pipeline to 

either a disposal or re-handling site. Mechanical removal methods typically produce dense, contaminated 

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material that is hauled by barge, railcar, truck/trailer, or conveyor systems. The feasibility and costs of 

transportation are frequently influenced by the scale of the remediation project. Key resources for 

information on transport methods are listed in Appendix D. 

Storage of contaminated sediment may also be necessary to dewater prior to upland disposal or to 

allow for pretreatment and equalization prior to treatment. For example, a temporary CDF may be 

designed to store material for periods when dredging or excavation is not possible due to weather or 

environmental concerns, while the treatment process may continue on a near 24-hour operating schedule. 

Storage may be temporary (e.g., pumping onto a barge with frequent off-loading) or more permanent 

(e.g., moving the sediment to a land-based CDF where it may be de-watered and treated). 

The project manager should consider potential contaminant losses to the water column and 

atmosphere during transportation to the treatment or disposal site, and temporary storage, if applicable. 

The risks of potential exposures during transport, through volatilization, water loss, or accidental spills 

during movement should also be evaluated. 

The risks associated with a temporary storage site are similar to those associated with CDFs, as 

discussed in section 6.7. In particular, in-water temporary CDFs can prove to be attractive nuisances, 

especially to waterfowl, by providing attractive habitat that encourages use of the CDF by wildlife and 

present the opportunity for exposure to contaminants. For highly contaminated sites, it may be necessary 

to provide a temporary cover or sequence dredging to allow for coverage of highly contaminated 

sediment with cleaner sediment to minimize short-term exposures. This method of control has proven 

effective for minimizing exposures at upland sanitary landfills. In addition, because some holding areas 

may not be designed for long-term storage of contaminated sediment, the risk of contaminant transport to 

ground water should be evaluated and monitored. 

6.6 TREATMENT 

The treatment of contaminated sediment is not usually a single process, but often involves a 

combination of processes to address various contaminant problems, including pre-treatment, operational 

treatment and/or effluent treatment/residual handling. 

Some form of pre-treatment and effluent treatment/residual handling are necessary at almost all 

sediment removal projects. A typical dewatering process is shown in Highlight 6-9. Sediment treatment 

processes of a wide variety of types have been applied in pilot-scale demonstrations, and some have been 

applied full-scale. However, the relatively high cost of most treatment alternatives, especially those 

involving thermal and chemical destruction techniques, can be a major constraint on their use at the 

present time (NRC 1997). The base of experience for treatment of contaminated sediment is still limited, 

as discussed in more detail later in this chapter. Each component of a potential treatment train is 

discussed below. 

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1 

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Highlight 6-9: Example of Dredging Dewatering Process 

6 6.6.1 Pre-Treatment

7

8 Pre-treatment modifies the dredged or excavated material in preparation for final treatment or

9 disposal. When pre-treatment is part of a treatment train, distinguishing between the two components

may be difficult and is not always necessary. Pre-treatment is generally performed to condition the 

11 material to meet the chemical and physical requirements for treatment or disposal; and/or to reduce the 

12 volume and/or weight of sediment that requires transport, treatment, or restricted disposal. Pre-treatment 

13 processes typically include dewatering and physical or size separation technologies. 

14 

Most treatment technologies require that the sediment be relatively homogeneous and that 

16 physical characteristics be within a relatively narrow range. Pre-treatment technologies may be used to 

17 modify the physical characteristics of the sediment to meet these requirements. Additionally, some 

18 pretreatment technologies may divide sediment into separate fractions, such as organic matter, sand, silt, 

19 and clay. Often the sand fractions contain lower contaminant levels and may be suitable for unrestricted 

disposal and/or beneficial use if it meets applicable standards and regulations. Selection factors, costs, 

21 pilot-scale demonstrations, and applicability of specific pre-treatment technologies are discussed in detail 

22 in EPA (1994b). 

23 

24 6.6.2 Operational Treatment 

26 Depending on the contaminant concentration and composition of the sediment, it may be 

27 advisable or necessary to treat the sediment to reduce the toxicity, mobility, or volume of the 

28 contaminants before disposal or final placement. In general, treatment processes have the ability to 

29 reduce sediment contaminant concentrations, mobility, and/or sediment toxicity by contaminant 

destruction or detoxification, extraction of contaminants from sediment, reduction of sediment volume or 

31 sediment solidification/stabilization. 

32 

33 Treatment technologies for sediment are generally classified as biological, chemical, extraction or 

34 washing, immobilization (solidification/stabilization), and thermal (destruction or desorption). In some 

cases, particle size separation is also considered a treatment technology. Pilot and full-scale treatment 

36 processes have been conducted at a variety of sites, although there is limited experience at Superfund 

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sites. Some of these sites are listed in Highlight 6-10. Additional information concerning treatment 

technologies for contaminated sediment may be found in U.S. EPA Office of Water’s Selecting 

Remediation Technologies for Contaminated Sediment (U.S. EPA 1993e) and other references listed in 

Appendix D. 

Bioremediation 

Bioremediation is the process in which microbiological processes are used to degrade or 

transform contaminants to less toxic or nontoxic forms. Bioremediation technologies harness this process 

by promoting the enzymatic production and microbial growth necessary to convert the target contaminant 

to non-toxic end products. Biological treatment has been used for decades to treat domestic and industrial 

waste waters. In recent years, it has been demonstrated as a technology for destroying some organic 

compounds in sediment. 

Microbial degradation of many persistent contaminants in the environment, such as PCBs and 

PAHs, may be influenced by the compound’s toxicity to microbial organisms; microbial feeding 

strategies, genetic ability to use the contaminant as a source of carbon and energy and the ability of 

microbes to propagate under site-specific environmental conditions. 

Bioremediation often attempts to alter the environmental conditions in the dredged or excavated 

material to stimulate the development of an appropriate microbial population. Such changes may include 

adjusting concentrations of nutrients or compounds, pH, oxygen concentration, temperature, or microbial 

population. The project manager should refer to EPA (1994b), Myers and Bowman (1999), and Myers 

and Williford (2000) for a summarization of bioremediation technologies and their application under sitespecific conditions. 

Chemical Treatment 

Chemical treatment refers to processes in which chemical reagents are added to the dredged or 

excavated material for the purpose of contaminant destruction. Contaminants may be destroyed 

completely, or may be altered to a less toxic form. Averett et al. (1990) reviewed several general 

categories of chemical treatment. Of the categories reviewed, the following treatments were considered 

most promising: 

• Chelation: Formation of a stable complex between a metal cation and a ligand (chelating 

agent), binding of the metal cation in this stable complex renders it unavailable for 

further reaction, efficiency varies with the chelating agent and dosage used (U.S. EPA 

1994b); 

• Dechlorination: Removes chlorine molecules from contaminants (e.g., PCBs and 

dioxins) through the addition of chemical agents under alkaline conditions and increased 

temperatures (U.S. EPA 1990b, and U.S. EPA 1990c). The process releases steam and 

volatile organic vapors and the vapors are further treated using activated carbon. The 

resulting products are generally less toxic than the original contaminants; and 

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Chapter 7: Dredging with Treatment or Disposal 

Highlight 6-10: Sediment Treatment Examples 

Country/Location Project Type Contaminants Process Options Scale R

BIOLOGICAL 

USA/WI Sheboygan River 

Remedial (Superfund) 

PCBs Contained land 

(sheet pile structure) 

Pilot F

Canada/ON Hamilton Harbor 

Remedial CSTTP 

PAHs Contained land Pilot W

c

Canada/ON 

Toronto Harbor 

Remedial CSTTP 

PAHs Bioslurry Pilot U

Netherlands Zeeland 

Navigation DPTP 

PAHs Land farming Pilot V

1

Milwaukee Harbor Navigation PAHs CDF Management/ Land 

farming 

Pilot M

CHEMICAL 

Canada/ON Hamilton Harbor 

Remedial CSTTP 

PAHs Reduction (thermal w/hydrogen) Pilot E

Netherlands Elburg 

Navigation DPTP 

PAHs Wet oxidation Pilot V

EXTRACTION 

USA/IN Gr. Calumet 

Remedial ARCS/SITE 

PCBs, PAHs Triethyl amine solvent Pilot U

USA/MA New Bedford 

Remedial SITE 

PCBs Supercritical propane Pilot U

NY/NJ Harbor Navigation Dioxins, PCBs, PAHs Organic solvent Pilot S

J

Canada/ON Toronto Harbor 

Remedial CSTTP 

Metals Acid extraction 

Chelation 

Pilot U

IMMOBILIZATION 

USA/NY Marathon Battery 

Remedial Superfund 

Metals Cd, Ni 

Stabilization Full S

c

Belgium 

Vilvoorde 

Metals Solidification Full 

USA/NY/NJ Harbor Navigation Metals, organics Stabilization Full S

J

USA/NY Buffalo River 

Remedial ARCS 

Metals Solidification (post-thermal 

desorption) 

Pilot U

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Chapter 7: Dredging with Treatment or Disposal 

Country/Location Project Type Contaminants Process Options Scale R

THERMAL 

USA/LA Bayou Bonfouca 

Remedial Superfund 

Creosote PAHs 

Incineration Full S

c

USA/IL 

Waukegan 

Remedial Superfund 

PCBs Thermal desorption Full H

USA/OH Ashtabula 

Remedial ARCS 

PCBs Thermal desorption Pilot U

USA/NY Buffalo River 

Remedial ARCS 

PAHs Thermal desorption Pilot U

Netherlands Elburg 

Remedial Metals Sintering Pilot V

USA/NY/NJ Harbor Navigation Dioxins, Metals, PCBs, 

PAHs 

Vitrification Pilot J

USA/NY/NJ Harbor Navigation Dioxins, Metals, PCBs, 

PAHs 

Rotary Kiln--Blended Cement Production 

Pilot J

PARTICLE SEPARATION 

USA/MI Saginaw River 

Remedial ARCS 

PCBs Metals 

Screens, Hydro cyclones 

Pilot U

Canada/ON Toronto 

Remedial CSTTP 

Metals PAHs 

Attrition scrubbers Hydro cyclones 

Pilot U

Germany Hamburg 

Navigation Metals 

PAHs, PCBs 

Screens, Hydro cyclones, Belt 

filter 

Full D

Canada/ON Welland 

Remediation CSTTP 

Metals Screens, Screw class, 

Centrifuge 

Pilot A

Netherlands Rotterdam 

Remediation Metals 

PAHs 

Hydro cyclones Settling basins 

Pilot D

13 14 15 16 17 18 19 20 21 22 23 24 

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• Oxidation (of organic compounds): Involves the use of chemical additives to transform 

and degrade organic contaminants. Oxidation may be commonly used to treat amines, 

phenols, chlorophenols, cyanides, halogenated aliphatic compounds, mercaptans, and 

certain pesticides in liquid waste streams (U.S. EPA 1991c). It may also be used on soil 

and sediment slurries and sludge (U.S. EPA 1994b). 

Specific applications, limitations, specifications, and efficiencies of these processes are discussed 

more fully in the ARCS Program’s Remediation Guidance Document (1994b). 

Extraction/Washing 

The primary application of extraction processes is to remove organic, and in some cases, metal 

contaminants from the sediment particles. Sediment washing is another term used to describe extraction 

processes, primarily when water may be a component of the solvent. In the extraction process dredged or 

excavated material is slurried with a chemical solvent and cycled through a separator unit. The separator 

divides the slurry into the three fractions: 1) particulate solids; 2) water; and 3) concentrated organic 

contaminants. The concentrated organics are removed from the separator for post-process treatment. 

Often the cycle is repeated several times before the treated solids are removed from the process. By 

separating the contaminants from the solids and water matrix, the extraction process can result in volume 

reductions of 20-fold or more (U.S. EPA 1994b). 

Pre-treatment is often necessary before solvent extraction in order to reduce oversized debris 

present in the dredged or excavated material. The maximum particle size depends on the scale and 

configuration of the extraction process, size is process specific and depends on size of equipment. 

Implementability for most of these processes may be difficult because of limited full-scale development 

for handling sediment and the problems of solvent recovery and potential toxicity of residual solvents. 

Immobilization 

Immobilization, commonly referred to as solidification/stabilization, alters the physical and/or 

chemical characteristics of the sediment through the addition of binders, including cements and pozzolans 

(U.S. EPA 1994b). Immobilization technologies primarily work by changing the engineering properties 

of the sediment so that contaminants are less prone to leaching. Alteration of the physical character of the 

sediment to form a solid material, such as a cement matrix, reduces the accessibility of the contaminants 

to water and entraps the contaminated solids in a stable matrix (Myers and Zappi 1989). The presence of 

free water in the original dredged or excavated material may be a large contributor to the initial leachate 

volume at a disposal site. By binding the free water into a hydrated solid, solidification reduces 

contaminant losses through leaching (U.S. EPA 1994b). 

Solidification with cement has been demonstrated for use on a large scale (greater than 1 million 

cubic yards) for New York/New Jersey Harbor dredged material (Myers and Adrian 2000). The material 

was used to cap a Brownfields site and a landfill that was subsequently used for a shopping mall. 

Chemical characteristics of the solidified sediment should be compatible with the environmental 

requirements of the reuse project (e.g., cement stabilized sediment may have elevated pH). 

Another form of immobilization, chemical stabilization, minimizes the solubility of metals 

primarily through the control of pH and alkalinity. In some cases, chemical stabilization technologies can 

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decrease the solubility of some metals, but increase the mobility of other metals (Myers and Zappi 1989). 

Anions, which may be more difficult to bind in insoluble compounds, may be immobilized by entrapment 

or micro-encapsulation. Chemical stabilization of organic compounds may be possible, but the 

mechanisms involved are not well understood (Myers and Zappi 1989). 

The potential for implementation of immobilization processes is better than other treatment 

processes because they are not as sensitive to process-control conditions. Stabilization processes have 

recently been used for contaminated New York Harbor sediment and at the Marathon Battery project. 

However, bench scale studies are recommended to ensure a successful project. For example, although 

solidification with lime is a simple process, the ensuing exothermic reaction can drive off volatiles, and/or 

create steam or dust problems. 

Thermal Treatment 

Thermal technologies include incineration, pyrolysis, thermal desorption, sintering, and other 

processes that require heating the sediment to hundreds or thousands of degrees above ambient 

temperatures. Thermal destruction processes, such as incineration, are effective for destroying organic 

contaminants, but are also expensive and have significant energy costs. Thermal treatment does not 

destroy toxic metals. There are chemical processes that destroy organic contaminants, such as reductive 

dechlorination, but these process are also expensive (and may have significant energy costs). 

Thermal desorption processes heat sediment to temperatures of 90°C to 540°C to physically 

separate volatile and semivolatile organic compounds from sediment. Water, organic compounds, and 

volatile metals are vaporized by the heating process and subsequently condensed and collected as a liquid, 

captured on activated carbon, or destroyed in an afterburner. Heating is accomplished using indirectly 

fired rotary kilns, heated screw conveyors, externally heated distillation chambers, or fluidized beds (U.S. 

EPA 1991d). The resulting volume of volatilized contaminants should be collected for subsequent 

treatment. 

The Superfund Innovative Technology Evaluation (SITE) program and New York Harbor, and 

Francingues and Thompson (2000) are evaluating two thermal treatment processes to remove enough 

contamination from the sediment for beneficial use purposes, such as aggregate. A specific SITE 

example is the Sediment Melter Technology Pilot-Scale study, which treated 70 tons of PCBcontaminated sediment from the Fox River, produce a glass aggregate material suitable as a foundation 

material. 

Particle Size Separation 

Particle size separation involves separation of the fine material from the coarse material by 

physical screening. A site demonstration of the Bergman USA (U.S. EPA 1994d) process resulted in the 

successful separation of less than 45 micron fines from washed coarse material and a humic fraction. As 

noted in the preceding paragraphs, particle size separation may serve as a pretreatment step prior to 

implementation of a treatment alternative. Many treatment processes require particle sizes of 1 cm or less 

for optimal operation. 

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Effluent Treatment/Residue Handling 

Treatment of process effluents (liquid/gas/solid) is a major consideration during selection, design, 

and implementation of dredging or excavation. As shown in Highlight 6-1, dredging or excavation may 

require management of several types of residual wastes from the pretreatment and operational treatment 

processes that include liquid and/or air/gas effluents from dewatering or other pretreatment/treatment 

processes, residual solids and runoff/discharges from active CDFs. 

These wastes can be handled through the use of conventional technologies for water, air, and 

solids treatment and disposal. However, the technical, cost, and regulatory requirements can be important 

considerations during the evaluation of dredging or excavation as a cleanup method. The project manager 

should refer to EPA (1994b) for a discussion of the implications and selection criteria for residual 

management. 

Information Resources for Treatment Technologies 

The list of potential sediment treatment technologies may continue to change as new technologies 

are developed and other technologies are improved. EPA has recognized the need for an up-to-date list of 

treatment alternatives and has developed the following databases: 

• EPA Remediation and Characterization Innovative Technologies (EPA REACH IT): 

Provides information on more than 750 service providers that offer almost 1,300 

remediation technologies and more than 150 characterization technologies (includes a 

variety of media, not just sediment). More information is available at 

http://www.epareachit.org/index3.html; and 

• Risk Reduction Engineering Laboratory (RREL) Treatability Database: Provides results 

of published treatability studies that have passed the EPA quality assurance reviews, it is 

not specific to sediment, and is available from the EPA’s Risk Reduction Engineering 

Laboratory, Cincinnati, Ohio, 45268 and at 

http://www.epa.gov/ncepihom/Catalog/EPA600C93003A.html. 

The NY/NJ Harbor Project is an example of a large-scale demonstration of dredged 

decontamination technologies. Each of the technologies presented in Highlight 6-11 has demonstrated 

destruction, removal, or immobilization of organic chemicals and metal contaminants and production of 

uncontaminated material that could be used in one or more commercial products such as manufactured 

cement, glass and ceramic tiles, facade bricks, and topsoil (Stern et al. 2000, Mulligan et al. 2001). 

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Highlight 6-11: NY/NJ Harbor - Treatment Technologies and Beneficial Use 

The goal of the NY/NJ Harbor Sediment Decontamination Project is to assemble a complete 

decontamination system for cost effective transformation of dredged material into an environmentally safe material 

used in the manufacturing of a variety of beneficial use products. 

The following four treatment technologies are being used at the NY/NJ site: 1) sediment washing; 2) 

thermal treatment; 3) solidification; and 4) vitrification. Each technology has a sponsor from the private sector that 

will provide the capital needed for facility construction and operation. 

Sediment washing (extraction) uses high-pressure water jets and proprietary chemical additives to extract 

both organic and inorganic contaminants from the sediment. The resulting materials can be used to produce 

manufactured soil for commercial, and in some cases, residential landscaping applications. The advantages to 

this treatment are modest capital costs and high throughput. A limitation to this treatment is that to be cost 

effective, the original sediment has to contain a significant amount of sand. 

A thermal treatment being used is a thermo-chemical manufacturing process that, at high temperatures, 

will destroy organic contaminants. The process will melt a mixture of sediment and modifiers, and the resulting 

product is a manufactured grade cement comparable to Portland Cement. This is a very effective treatment, but 

expensive. 

A third process is a “treatment train” that includes dewatering, pelletizing, and transport to an existing 

light-weight aggregate facility. Pelletizing is a type of solidification treatment. After the sediment is dewatered, it is 

mixed with shale fines and extruded into pellets. The pellets are fed into a rotary kiln, and the organic matter 

explodes. The resulting material can be used as a structural component in concrete, insulation (pipeline) and for 

other geotechnical uses. 

Finally, the process includes a high temperature vitrification, which uses an electrical current to heat 

(melt) and vitrify the soil in place. This process can destroy organic contaminants and incorporate metals into a 

glassy matrix which can be used to produce an architectural tile. 

Source: Stern et al. 2000, Mulligan et al. 2001, Stern 2001, NRC 1997 

6.7 DISPOSAL 

Disposal refers to the placement of dredged or excavated material and process wastes into a 

temporary or permanent structure, site, or facility. The goal of disposal is to prevent contaminants 

associated with sediment and/or residual wastes from reentering the environment and impacting human 

health and the environment. Disposal is a major component of any dredging or excavation alternative. 

The identification of disposal sites may often be the most controversial component of planning, design, 

and implementation. 

Contaminated sediment is typically managed in upland sanitary landfills, hazardous or chemical 

waste landfills, CDFs, or CADs. Also, the material may have a beneficial use in an environment other 

that the aquatic ecosystem from which it was removed (e.g., foundation material beneath a newly 

constructed Brownfields site), especially if the sediment has undergone treatment. 

Highlight 6-12 provides summary descriptions and extent of use for each of these technologies. 

Additionally, the EPA (1994b) provides a discussion of the available technologies, including an in-depth 

discussion of costs, design considerations, and selection factors associated with each technology. Averett 

et al. (1990), EPA (1991b), and Palermo and Averett (2000) provide additional discussion of disposal 

options and considerations. 

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Chapter 6: Dredging and Excavation 

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Highlight 6-12: Summary of Disposal Technologies 

Technology Description Use 

Sanitary Landfill Dewatered material disposed of in a 

properly licensed landfill. 

Commonly used for disposal of 

dredged material and 

pretreatment/treatment process 

residuals. 

4 Hazardous/Chemical Waste 

5 Landfill 

6 Confined Disposal Facilities 

7 Level-Bottom Capping 

8 Contained Aquatic Disposal 

Highly contaminated, dewatered 

material disposed of in a landfill 

specially licensed to accept hazardous 

and chemical wastes. 

In-water or upland, diked facility 

specifically constructed for disposal of 

dredged material. 

Material placed on a flat bottom of a 

waterbody and covered with a layer of 

clean sediment. 

Material placed into an excavated or 

natural depression or underwater diked 

area and covered with clean material or 

cap. 

Commonly used for disposal of 

dredged material and 

pretreatment/treatment process 

residuals. 

Routinely used for disposal of raw 

dredged material from 

navigational and remedial 

projects. 

Used for disposal of contaminated 

sediment from navigational 

dredging within Clean Water Act 

(CWA) 404 jurisdiction. 

Used for disposal of contaminated 

sediment from navigational and 

environmental dredging within 

CWA 404 jurisdiction. 

Beneficial Use Lightly contaminated, raw or treated 

material used for construction, beach 

nourishment, or other beneficial uses. 

Used infrequently in 

environmental dredging projects; 

may be appropriate for treated 

sediment. 

10

11 6.7.1 Sanitary/Hazardous Waste Landfills

12

13 Existing commercial and municipal sanitary and hazardous waste landfills are one of the most

14 widely used options for disposal of dredged or excavated material and pre-treatment/treatment residuals

15 associated with environmental dredging and excavation. Landfills may also be constructed specifically

16 for use in disposing of sediment from environmental dredging. Landfills can be categorized by the types

17 of wastes they accept and the laws regulating their operation. Most solid waste landfills accept all types

18 of waste (including hazardous substances) that are not regulated as Resource Conservation and Recovery

19 Act (RCRA) hazardous waste or Toxic Substances Control Act (TSCA) toxic materials. Additionally, a

20 limited number of RCRA-hazardous and TSCA-toxic landfills may be available for disposal of hazardous

21 and toxic materials (U.S. EPA 1994b).

22

23 Due to the restriction on liquids in landfills, most dredged material should be de-watered and/or

24 stabilized/solidified before disposal in a landfill. Temporary placement in a CDF or pretreatment using

25 mechanical equipment may therefore be necessary (Palermo 1995).

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Chapter 6: Dredging and Excavation 

1 6.7.2 Confined Disposal Facilities

2

3 CDFs are engineered structures enclosed by dikes and specifically designed to retain dredged

4 solids and associated contaminants. Under normal operations, water is discharged over a weir structure or

5 allowed to migrate through the dike walls while solids are retained within the CDF. Typically effluent

6 guidelines or discharge permits govern the monitoring requirements of the return water. Details regarding

7

8 Engineers (USACE) engineer manual, Confined Disposal of Dredged Material (USACE 1987).

9

10 A cross-sectional view of a typical nearshore CDF dike design is shown in Highlight 6-13. CDFs

11 may be located either upland (above the water table), near-shore (partially in the water), or completely in

12 the water (island CDFs). EPA (1996f), EPA (1994b), EPA (1991b), and Averett et al. (1990) contain

13 thorough descriptions, technical considerations, and costs associated with CDFs. Additionally, Black and

14 Veatch (in preparation) contains a history and evaluation of the design and performance of CDFs in the

15 Great Lakes Basin, including a review and discussion of relevant contaminant loss and contaminant

16 uptake studies.

18 

19 

the engineering design of CDFs to include sizing to retain solids are available in the U.S. Army Corps of 

Disposal Side Lake Side 

Granular Fill 

16' 

8' Sand Filter

5' 

1' 

1.5' 

1' 

2' 

1.5' 

1' 

1.5' 

1' 

Note: 1ft. = 0.3m 

Steel Sheet Piling 

Highlight 6-13: Cross Section of a Confined Disposal Facility Dike with a Filter Layer 

20 

21 Note: Adapted from US. EPA 1998d 

22 

23 

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6.7.3 Contained Aquatic Disposal 

Contained aquatic disposal is a type of subaqueous capping in which the contaminated dredged 

material is placed into a natural or excavated depression. The depression provides lateral containment of 

the contaminated material, and also has the advantage of requiring less maintenance and being more 

resistant to erosion than level-bottom capping. The depression for the CAD cell may be excavated using 

conventional dredging equipment or natural or historically dredged depressions may be used. 

Uncontaminated material excavated from the depression may subsequently be used for the cap (U.S. EPA 

1994b). The design of a CAD option for a sediment remedy should be approached in the same way as a 

CAD project design for dredged material disposal and cap designs for in-situ capping (U.S. EPA 1998d, 

Palermo et al. 1998a, and Palermo 1997). A major consideration is the selection of the appropriate 

methods for placement of the contaminated material and subsequent placement of the cap. Community 

acceptance and local land use laws are also important considerations in the siting and placement of CADs. 

6.7.4 Losses From Disposal Facilities 

Evaluation of a disposal facility for placement of contaminated sediments should include 

assessment of contaminant migration pathways and incorporation of management controls in the facility 

design as needed. Landfill disposal options may have short-term releases which include spillages during 

transport and volatilization to the atmosphere as the sediment is drying. As for any disposal option, 

longer-term releases depend in large part on the characteristics of the contaminants and the design and 

maintenance of the facility. 

For CDFs, contaminants may be lost via effluent during filling operations, surface runoff due to 

precipitation, leachate through the bottom, seepage through the dike wall, volatilization to the air, and 

uptake by plants and animals. The USACE has developed a suite of testing protocols for evaluation of 

each of these pathways (U.S. EPA and USACE 1992), and these procedures are included in ARCS 

guidance for estimating contaminant release (U.S. EPA 1996f). The USACE is developing a 

comprehensive contaminant pathway testing and evaluation manual for CDFs (USACE in preparation). 

Depending on the likelihood of contaminants leaching from the confined sediment, a variety of dike and 

bottom linings and cap materials may be used to minimize contaminant loss (U.S. EPA 1991b, U.S. EPA 

1994b, Palermo and Averett 2000). CDFs for sediment remediation projects are more likely to need 

control measures such as bottom or sidewall liners or low permeability dike cores than would CDFs 

constructed for navigation dredged material. 

For CADs, contaminants maybe lost to the water column during placement of the contaminated 

sediment, and advection of pore water during the initial consolidation of the sediment following 

placement and capping. Volatilization may also occur at both CDFs and CAD sites during placement. 

Whatever disposal options are evaluated, the effects of contaminant losses during construction and in the 

long term should be considered. 

6.7.5 Beneficial Use 

Beneficial use of dredged or excavated sediment has been implemented infrequently to date as a 

dredge material management option in association with environmental cleanup. Although not normally 

considered a disposal option, in special situations, beneficial use may be an appropriate management 

option for lightly contaminated or treated sediment resulting from environmental dredging projects. 

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Significant cost saving may be realized if physical and chemical properties of the sediment allow for 

beneficial use. In each case, the contaminant levels and environmental exposure, including considerations 

of future land use, should be assessed. For example, at Newburgh Lake, Michigan, significant cost 

savings were realized by using lightly contaminated dredged material as daily cover at a local sanitary 

landfill, where the presence of the dredged material did not pose risk within the landfill boundary. 

Options for beneficial use may include the following: 

• Beach nourishment (for a clean sand fraction); 

• Construction fill; 

• Sanitary landfill cover as in the above example; 

• Mined lands restoration (e.g., 

http://www.dep.state.pa.us/dep/DEPUTATE/MINRES/BAMR/bark_camp/barkhomepage 

.htm); 

• Subgrade cap material (topped with clean sediment or other fill); or 

• Building materials (e.g., architectural tile, see Highlight 6-11). 

A series of technical notes on beneficial use of contaminated material is currently being 

developed by the USACE (Lee 2000). Use of contaminated materials from CDFs (to include treated 

material) is a major thrust of the USACE Dredging Operations and Environmental Research (DOER) 

program (http://www.wes.army.mil/el/dots/doer/). 

In some cases, a CDF can be integrated with site reuse plans to both reduce environmental risk 

and simultaneously foster redevelopment in urban areas and Brownfield sites. For example, at the Sitcum 

Waterway cleanup project in Tacoma, Washington, contaminated sediment was placed in a near shore fill, 

which was then developed into a container storage area. Also, there may be innovative and 

environmentally protective ways to reuse dredged contaminated sediments in habitat restoration projects 

(e.g., placement of lightly contaminated material over highly contaminated materials to build up 

elevations necessary for final placement of clean emergent marshlands). 

6.8 SITE CONSIDERATIONS 

6.8.1 Physical Environment 

Several aspects of the physical environment may make dredging more or less difficult to 

implement. In the remedial investigation, the following types of information should be collected, as they 

will affect the type of equipment selected and potentially the feasibility of dredging: 

• Bathymetry, slope of the sediment surface and water depth; 

• Currents and tides; 

• Bottom conditions, especially the presence of debris and large rocks; 

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• Depth to and (un)evenness of bedrock or hard bottom (e.g., stiff glacial till); 

• Sediment particle size distribution and degree of consolidation; 

• Thickness of contaminated sediment; 

• Distance between dredging and disposal locations; 

• The presence of structures such as piers, pilings, cables, or pipes; and 

• Land access to waterbody. 

Additionally, sediment removal may change the hydrodynamics and slope stability of the 

remediation area. These changes need to be evaluated to insure that the removal activity does not cause 

instability or other adverse effects on the system. 

6.8.2 Sediment Characteristics 

Thorough horizontal and vertical characterization of both the physical sediment characteristics 

and the contaminants at the site is needed during the remedial investigation to evaluate the feasibility of 

dredging or excavation. The results of this characterization will help determine the area, depth, and 

volume to be removed, and the volume of sediment requiring treatment and/or disposal. Some aspects of 

sediment characterization are discussed in Chapter 2, Remedial Action Considerations. 

There are several tests that may help provide the project manager with needed information for 

design of dredging, treatment, or disposal methods. The project manager should refer to Highlight 6-14 

for a summary of the most commonly used tests. In addition, the time and cost needed to conduct 

engineering and environmental testing should be considered. Several guidance documents on estimating 

contaminant losses from dredging and disposal have been developed by the EPA and USACE. The 

project manager should refer to Estimating Contaminant Losses from Components of Remediation 

Alternatives for Contaminated Sediments (U.S. EPA 1996f), Evaluation of Dredged Material Proposed 

for Discharge in Waters of the U.S. - Testing Manual (Inland Testing Manual) (U.S. EPA and USACE 

1998) and Evaluation of Dredged Material Proposed for Disposal at Island, Nearshore or Upland 

Confined Disposal Facilities - Testing Manual (USACE in preparation) for further information. 

6.8.3 Waterway Uses and Infrastructures 

Removal of contaminated sediment has the advantage of potentially imposing fewer limitations 

on waterway uses than capping or monitored natural recovery alternatives. However, any evaluation of 

the feasibility of a dredging or excavation project should consider impacts to existing and potential future 

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Highlight 6-14: Dredging/Disposal Feasibility Tests 

Test Description Data Utilization Reference 

Atterberg Limits 

Determines the percent moisture content 

that sediment changes from a solid to a 

semi-solid (shrinkage limit), a semi-solid 

to a plastic (plastic limit), and a plastic to 

a liquid (liquid limit). 

Used in conjunction with other physical 

properties to determine the potential 

physical behavior of the sediment during 

remediation; for example, at moisture 

contents greater than the liquid limit, the 

sediment may behave and flow like a 

viscous liquid. 

Spigolon 1993 

Pancake Column 

Leach Test (PCLT) 

Water is passed through a sample of the 

dredged material; after passing through 

the dredged material, the water is 

analyzed for contaminant concentrations. 

Used with mass transport modeling to 

estimate the long-term water quality 

impact and contaminant flux in a 

confined disposal site. 

Brannon et al. 1994 

Dredged Material 

Slurry Settling Tests 

Sediment slurry/coagulant mixtures are 

added to a settling column; height of the 

sediment/water interface is measured at 

specific time intervals over a period of 

time. 

Performed to observe the settling 

behavior of sediment; aids in design of 

particle settling basins, confined 

disposal facilities, and sediment 

dewatering system. 

USACE 1987 

Effluent Elutriate Test 

Aqueous extract is prepared from a 

sediment/water mixture that is mixed and 

allowed to settle; the extract is analyzed 

for its contaminant concentrations 

(Settling time = Estimated CDF water 

retention time). 

Used to estimate the amount of 

contaminants that may be released 

during hydraulic filling of a confined 

disposal facility. 

USACE WES 1998 

Moisture Content 

A measure of the amount of moisture in a 

soil sample, calculated as: (wet weight -

dry weight)/(dry weight); commonly used 

in engineering and geological 

applications. 

Used in conjunction with other physical 

properties when designing and sizing 

remediation components. 

ASTM D2216 

Particle Size 

Distribution 

Particles are separated into various size 

classes, such as sand, silt, clay, by 

passing them through a series of 

fine-meshed sieves. 

Determines the relative amounts of silts, 

sands, and clay materials in sediment; 

has a wide range of implications for 

pretreatment, treatment, etc. 

Spigolon 1993 

Specific Gravity 

Measurement of the weight of a volume 

of sediment compared to the same 

volume of water. 

Useful in determining how quickly 

sediment will sink in water; useful in 

design sediment dewatering and particle 

size separation systems. 

U.S. EPA and 

USACE 1998 

Standard Elutriate 

Test 

An aqueous extract is prepared from a 

sediment/water mixture that is allowed to 

settle for one hour, centrifuged, and 

decanted; extract is analyzed for its 

contaminant concentrations. 

Used to estimate the amount of 

contaminants that may be released 

during dredging and open water 

disposal. 

U.S. EPA and 

USACE 1977 

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16 uses of a waterway. Waterway uses that should be considered when selecting a dredging with treatment 

17 or disposal alternative include the following:

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21 • Residential/commercial/military moorage;

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23 • Flood control;

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25 • Recreation;

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Chapter 6: Dredging and Excavation 

• Fishing; 

• Water supply, such as presence of intakes; 

• Storm water or effluent discharge outfalls; 

• Use by fish and wildlife, especially sensitive or important aquatic habitats; 

• Waterfront development; 

• Utility crossings; 

• Existing disposal sites; and 

• Anchorage areas. 

Evaluation of the feasibility of a sediment removal project should include an analysis of whether 

impacts to these uses may be avoided or minimized both during construction and in the long term. For 

dredge or fill projects being considered within or adjacent to a navigation or flood control channel, the 

long- and short-term effects of the project on the functions of the channel should be considered. The 

acceptable draft of vessels allowed to navigate over a contained aquatic disposal should consider water 

level fluctuations (seasonal, tidal, and wave) and the potential effects of grounding on a cap. Because of 

the potential erosion caused by propeller wash, restrictions on propeller size and/or vessel draft may be 

necessary. Anchoring or bottom trawling should not be allowed at locations on or near the contained 

aquatic disposal site to avoid disturbance of a cap. 

6.8.4 Habitat Alteration 

The project manager should consider the potential impact of habitat loss or alteration in 

evaluating a dredging or excavation alternative. While a project may be designed to minimize habitat 

loss, or even enhance habitat, sediment removal and disposal does alter the environment. However, it is 

important to determine whether the loss of a contaminated habitat is a greater impact than the benefit of 

providing a new, modified but less contaminated habitat. For example, a sediment removal alternative 

may or may not be appropriate where extensive damage to an existing upland or wetland will occur. If 

the contaminated sediment in the wetland is bioavailable and may be impacting wildlife populations, the 

short-term disruption of the habitat may be warranted to limit ongoing long-term impacts to wildlife. In 

this instance, the contaminated habitat as an attractive nuisance may more than offset its positive 

functional values. On the other hand, if the wetland is functioning properly and is not acting as a 

contaminant source to the biota and the surrounding area, it may be appropriate to leave it intact rather 

than remove it. Deliberations as to whether to alter wetland and aquatic habitats should be a routine 

component in the remedial decision process, and each site offers its own unique considerations. 

Coordination with natural resource agencies will assist the project manager in determining if the dredging 

project may impact aquatic organisms or their habitat, and how to minimize these impacts. 

Another consideration is avoidance of short-term ecological impacts during dredging. This may 

involve timing the project to avoid water quality impacts during migration and breeding periods of 

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Chapter 6: Dredging and Excavation 

sensitive species or designing the dredging project to minimize suspended sediment during dredging and 

disposal. 

Habitat impacts are also important when evaluating disposal options. Near shore habitat is often 

the most sensitive and important habitat to aquatic organisms, and, in many cases, has already been 

adversely affected by human activity. Filling these areas should be considered only if no other options 

with less adverse effect on the aquatic environment are available. Examples of projects where filling of 

wetlands was deemed appropriate to achieve cleanup goals include the Bailey Waste site in Texas City, 

Texas, where the Record of Decision (ROD) called for filling in marsh areas to make a causeway for 

excavation equipment to access contaminants that extended from the shoreline out into the marsh. At the 

New Bedford Harbor, Massachusetts site, a dewatering facility may be constructed in a shoreline area 

which may also be available for port activities in the future. New Bedford decisions preserve an 

extensive salt marsh system on the opposite side of the estuary. 

Highlight 6-15 presents some general points to remember from this chapter.

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Highlight 6-15: Points to Remember When Considering Dredging and Excavation 

• Source control generally should be implemented to prevent re-contamination 

• A dredging or excavation alternative should include details concerning all phases of the project, including 

sediment removal, transport, and treatment or disposal options 

• Transport and disposal options may be complex and controversial; start investigating options early and 

discuss them with stakeholders 

• In predicting risk reduction effects of dredging or excavation of deeply buried contaminants, the project 

manager should remember that biota will only respond to removal of contaminants that are bioavailable 

• Environmental dredging should be conducted to take advantage of new equipment and methods of 

operation which minimize resuspension 

• Project managers should conduct a site-specific assessment of anticipated sediment resuspension, 

contaminant release and transport, and its potential ecological impacts prior to dredging 

• Project managers should make realistic assumptions regarding residual contamination. Where overdredging is not possible, residual contamination is generally higher than where this practice is possible 

• Excavation (conducted in the dry) often leads to lower levels of residual contamination than dredging 

(conducted under water) 

• The use of experienced operators and oversight personnel skilled in dredging or excavation technologies 

as well as other phases of the project is very important to an effective cleanup 

• A dredging or excavation project should be monitored during implementation to assess resuspension and 

transport of contaminants, immediately after implementation to assess residuals, and after 

implementation to measure long-term recovery of biota and test for re-contamination 

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