COMMENCEMENT BAY NEARSHORE/TIDEFLATS
SUPERFUND SITE, TACOMA, WASHINGTON
REMEDIAL INVESTIGATIONS
Evaluation of Alternative Dredging
Methods and Equipment, Disposal
Methods and Sites, and Site Control
and Treatment Practices for
Contaminated Sediments
PREPARED FOR:
WASHINGTON STATE
DEPARTMENT OF ECOLOGY
JUNE 1985
PREPARED BY:
US Army Corps
of Engineers
Seattle District
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SECURITY CLASSIFICATION OF THIS PAGE (When Data Entered)
REPORT DOCUMENTATION PAGE
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1. REPORT NUMBER
2. GOVT ACCESSION NO.
3. RECIPIENT'S CATALOG NUMBER
4. TITLE (and Subtitle)
Evaluation of Alternative Dredging Methods and
Equipment, Disposal Methods and Sites, and Site
Control and Treatment Practices for Contaminated
Sediments
S. TYPE OF REPORT & PERIOD COVERED
Final Report
6. PERFORMING ORG. REPORT NUMBER
7. AUTHORfs)
Keith E. Phillips, John F. Malek,
W. Burton Hamner
8. CONTRACT OR GRANT NUMBERS.)
9. PERFORMING ORGANIZATION NAME AND ADDRESS
U.S. Army Corps of Engineers, Seattle Distr ict
P.O. Box C-375r>
Wnqhi mjfnn 9 1 ? 1 - ^ 7 r> ^
10. PROGRAM ELEMENT, PROJECT, TASK
AREA a WORK UNIT NUMBERS
H. CONTROLLING OFFICE NAME AND ADDRESS
Environmental Resources Section
U.S. Army Corps of Engineers, Seattle District
P.O. Box C-3755, Seattle Washington 98124-3755
12. REPORT DATE
June 1985
13- NUMBER OF PAGES
277
!«. MONITORING AGENCY NAME fit ADDRESS^// different Iron Controlling Office)
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18. SUPPLEMENTARY NOTES
19. KEY WOROS (Continue on reverse tide il neceeaary and Identity by block number)
Dredging Alternative technologies Contaminant Containment
Disposal Contaminated Sediments
Treatment Chemical toxicity
20. ABSTRACT (Caathme «n rerermm eixte ft treceaeary and Identify by block number)
Alternative technologies and techniques for dredging, disposal, and treatment
of contaminated sediments are reviewed. Implications of alternative techno-
logies for management of contaminated sediments are discussed. Selection of
appropriate technologies for contaminated sediments management depends on the
physical and chemical profile of the sediments, and v on the
physical state (liquid, solid, or gaseous) of contarr
RXDDDDDlflflfl
DD 1473 EMTIO* ' ' MOV 65 IS OBSOLETE
SECURITY CLASSIFICATION OF THIS PAGE (When Dat* Entered)
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SECURITY CLASSIFICATION OF THIS PAGE(TOian Dmf BnUfd)
changes in state that may occur at different phases of dredging, disposal,
contitol, and treatment. Determination of acceptable criteria governing
concentrations of contaminants in water, sediments and soils, and air is the
major requirement for selecting specific technologies for managing contam-
inated sediments. Technologies should be used which ensure that criteria
will be met at all phases in the handling operations. Cost is most variable
for disposal site effluent treatment options.
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COMMENCEMENT BAY NEARSHORE/TIDEFLATS
SUPERFUND SITE, TACOMA, WASHINGTON
REMEDIAL INVESTIGATIONS
EVALUATION OF ALTERNATIVE DREDGING METHODS AND EQUIPMENT,
DISPOSAL METHODS AND SITES, AND SITE CONTROL AND TREATMENT
PRACTICES FOR CONTAMINATED SEDIMENTS
PREPARED FOR:
WASHINGTON DEPARTMENT OF ECOLOGY
OLYMPIA, WASHINGTON
PREPARED BY:
SEATTLE DISTRICT
U.S. ARMY CORPS OF ENGINEERS
SEATTLE, WASHINGTON
MARCH 1985
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ACKNOWLEDGEMENTS
Funding for this work was provided by the State of Washington Department of
Ecology, acting under cooperative agreement with the U.S. Environmental
Protection Agency for the remedial investigations of the Commencement Bay
Nearshore/Tideflats Superfund Site. In addition, substantial technical
assistance and information synthesis required for this report were provided by
the Environmental Engineering Division and the Ecosystem Research and
Simulation Division of the Waterways Experiment Station, U.S. Army Corps of
Engineers. This assistance was provided under auspices of the Dredging
Operations Technical Support Program (DOTS).
i
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EXECUTIVE SUMMARY
The State of Washington Department of Ecology (WDOE) has entered into a
cooperative agreement with the U.S. Environmental Protection Agency to act as
lead agency in the implementation of Phase I Remedial Investigations for the
Commencement Bay Nearshore/Tideflats Superfund Site, Washington. Superfund
remedial action may involve removal and handling of contaminated sediments
found in the bay. In addition, ongoing and proposed navigation activities in
Commencement Bay require dredging and disposal of contaminated sediments
located in the nearshore areas. As a result, Superfund site investigations
and planning of navigation projects require identification and evaluation of
alternative methods for dredging and disposal of contaminated sediments. By
agreement with WDOE, the Seattle District, U.S. Army Corps of Engineers, pre-
pared this report to describe and evaluate alternative dredging methods and
equipment, disposal methods and sites, and site control and treatment practices
for contaminated sediments derived from Commencement Bay. These alternatives
are evaluated based on the following factors:
o Cost of each alternative.
o Degree of confinement and release of volatile, soluble, and sediment-
bound contaminants resulting with each alternative.
o Considerations and limitations specific to each alternative (e.g.,
equipment and site availability, method efficiency, equipment depth limita-
tions, sociopolitical concerns, and other indicators of practicability).
Dredging methods and equipment are evaluated in terms of availability, pro-
duction rates, and contaminant containment during use. Characteristics,
operational considerations and control, and-equipment considerations and
modifications for dredging contaminated sediments are described for each
dredging alternative. The two basic types of dredges addressed in this
report, hydraulic and mechanical dredges, are categorized based on the simi-
larities each have in terms of contaminant loss during dredging. Special-
purpose dredges that have been designed for contaminated sediments are
included in the hydraulic dredge category.
Three generic disposal methods, open-water, upland, and nearshore, are
examined in terms of their strengths and weaknesses in successfully containing
the various contaminant classes. Specific potential disposal sites in the
Commencement Bay area, identified for this report, are discussed and evaluated
for their ability to meet the anticipated needs for disposal of contaminated
sediments. Additionally, options and limitations for offsite disposal are
briefly addressed.
Site control measures and treatment practices addressed in this report pertain
to contaminant confinement within a selected area, isolation from the environ-
ment, and removal from liquid or gas effluents during and after disposal of
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contaminated sediments. In addition to site control and treatment, discus-
sions are presented on biological control of disposal areas and appropriate
monitoring requirements for each disposal method, as well as remedial response
to monitoring indications.
The costs of alternative dredging methods, disposal options, and treatment
methods are discussed in chapter 5. This chapter describes the principles and
ranges of costs for the technologies and procedures discussed in this report
and illustrates comparisons between various technologies and management options
on the basis of cost. Little cost information is available for the applica-
tion of treatment technologies due to the scarcity of investigations on the
applicability to treatment of dredged materials and the many site-specific
factors involved. Therefore, the costs of treatment at various levels of con-
taminant removal are estimated for representative upland and nearshore sites,
in order to illustrate cost factors affecting decisions concerning appropriate
treatment levels, and disposal areas.
In chapter 6.0 this report compares and discusses these various alternatives,
presenting those conclusions that can be formulated at this stage of planning
for Commencement Bay. First, preferred dredging methods and possible trade-
offs for various types of sediment contamination are addressed. Disposal
methods are ranked in terms of the major factors that would influence decisions
on disposal of contaminated sediments. The likely applicability of treatment
methods to Commencement Bay is discussed. Second, the relative contaminant
loss or confinement obtained during each stage of the handling process (dredg-
ing, disposal, control, and treatment) is discussed. Third, disposal sites
are evaluated and recommendations on preferred or most appropriate sites for
near-term consideration are presented. Fourth, information needs and data
gaps for handling of contaminated sediments are identified. Research or tests
that merit priority consideration at this time are discussed. In addition, as
a way of highlighting key steps and considerations in selecting dredging and
disposal methods, available information is applied to a case study contami-
nated sediment from Commencement Bay.
In terms of sediment resuspension at the dredge site, special-purpose hydraulic
dredges produce less resuspension than conventional hydraulic dredges, and
with the exception of hopper dredge overflow, conventional hydraulic dredges
produce less resuspension than mechanical dredges. In terms of slurry water
that may require treatment at the disposal site, mechanical dredges produce
much less water than special-purpose hydraulic dredges, and special-purpose
dredges produce less water than conventional hydraulic dredges. Hydraulic
dredges produce less solids resuspension at the dredging site and have a
higher removal efficiency for liquid and solid phases than do mechanical
dredges. However, use of a hydraulic dredge to obtain high removal efficiency
at the dredging site involves a tradeoff requiring consideration of increased
slurry water and sediment consolidation time at the disposal site.
Different dredging methods appear more appropriate for certain contaminant
classes:
o For volatile contaminants, mechanical dredges are likely to produce
less loss than hydraulic dredges.
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o Sediment-bound contaminants can be removed more efficiently by hydraulic
dredges than by mechanical dredges and appropriate technology exists for con-
trol of solids at the disposal end.
o Soluble contaminants can be removed more efficiently by a hydraulic
dredge, but are difficult to control at the disposal end and treatment of the
effluent water may be required.
Most projects are likely to contain all three types of contamination, con-
founding a decision on appropriate dredging technique. In terms of overall
contamination, sediment-bound contaminants usually represent the bulk of the
contamination, suggesting use of hydraulic equipment for maximum recovery and
extraction efficiency. The amount of volatiles that may be lost during dredg-
ing are not likely to be a source of major concern in many projects. As the
types and amount of soluble, or easily solubilized, contaminants increase in a
sediment to be dredged, greater consideration should be given to the cost and
environmental impact of mechanical dredging with watertight equipment relative
to that of hydraulic dredging and water treatment at the disposal site~ This
evaluation is likely to be the key to selecting a dredge for a given contami-
nated sediment.
A variety of dredging equipment modifications are appropriate for work in
contaminated sediments. Modifications that appear most promising at this time
include:
o the walking spud (hydraulic dredge),
o ladder pumps (hydraulic dredge),
o in-line production meters (hydraulic dredge),
o large, watertight buckets (mechanical dredge), and
o degasser collection and treatment (in dredge furnace or other) system
(hydraulic dredge).
Operational modifications to be considered for hydraulic cutterhead dredges
include minimizing cutter revolution speed, controlling swing speed, and not
overdigging the maximum cut depth. For mechanical dredging, sweeping the
bottom with the bucket and digging fine-grained sediments from underneath
(heavy buckets penetrating through soft surface materials) are practices to be
avoided in contaminated areas. For most operator controls or operational
modifications, serious consideration should be given to hourly rental of
dredging equipment rather than bidding in order to maintain control of project
costs and better define cost factors during first-time use of modifications.
The key considerations involved with disposal method effectiveness are:
o the class of contaminants of concern,
o the similarity of the disposal site condition to in situ conditions,
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o the number and magnitude of contaminant transport mechanisms operating
at the disposal site,
o the degree of control or treatment possible to intercept migrating
contaminant fractions, and
o the risk of significant adverse effects from contaminants released by
the disposal method.
Heavy metals often will go into solution and become mobile in oxidized,
unsaturated sediments (e.g., in an upland site). Organic contaminants tend to
remain partially soluble regardless of how wet or dry the sediment stays.
Therefore, they will have greater mobility where greater exchange of water
within the sediments occurs. Nearshore sites have greater water exchange than
upland, and upland has greater exchange than open water. These tendencies
would suggest that heavy metal contamination be left under water and con-
sideration be given to placing organics contamination above water.
In general, leaving, or disposing of, contaminated sediments in a chemical
environment as close as possible to their in situ state favors contaminant
retention (especially metals). Geochemical changes associated with air and
oxygen in upland and nearshore sites can change sediment pH (mobilizing
metals) and alter (dissolve, degrade, or volatilize) sediment organic carbon
(mobilizing organics). Based on this, many contaminants would tend to stay
bound to sediments better in an open-water, capped site than a nearshore or
upland site. (For organic contaminants, the influence of geochemical changes
may be outweighed by the consideration of water exchange.)
Open-water sites, especially those in deep water, have fewer transport
mechanisms (e.g., air is absent) than upland sites. Nearshore sites have the
most transport routes available and are located in a very active environment;
therefore, nearshore disposal is the least preferred method for long-term
confinement of contaminants.
In terms of controlling contaminant release, open-water disposal allows for
very few controls of releases other than cap thickness. However, increasing
cap thickness is a relatively simple and effective control method. Upland
disposal, on the other hand, allows for the greatest control through design
features, monitoring capabilities , backup contaminant intercept systems, and
treatment facilities. The nearshore disposal option does allow for some
greater control of contaminants than in open water, but many fewer than are
available in an upland situation.
For open-water disposal, the levels of contaminant concentration released will
be low relative to nearshore or upland sites and will be diluted by the over-
lying water. The risk of significant damage in this environment is low and
would not likely affect human health. For upland disposal, environmental
risks incurred may be higher than in open water because of potential human
health concerns. For nearshore disposal, the risks to the environment and to
human health are much greater than in open water and in many situations are
greater than at an upland site.
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As an overall generalization, and looking ahead to development of criteria for
appropriate disposal methods, the interplay of site control and contaminant
mobility suggests that nearshore sites should receive the low-level contamina-
tion, open-water sites the low-to-medium-level contamination, and upland sites
the high-level contamination.
In going from upland to nearshore to open-water disposal, the degree of site
control and the number of available treatment options decreases. This
decreasing control is translated into reduced opportunities to design addi-
tional treatment measures that would prevent sudden or accelerated contaminant
releases into the environment and/or to avoid the extreme expense of sediment
removal and relocation.
Potential treatment at upland sites includes several methods that cannot be
implemented at nearshore sites without site dewatering. Dewatering would
require extraordinary and extremely expensive construction techniques and is,
therefore, not considered here. Foundation material in the nearshore zone may
not be adequate to support the necessary diking. Seismic potential, mud
foundations, and tidal fluctuations can threaten dike stability. As a result,
construction in the nearshore zone has a higher risk of failure. Therefore,
equivalent treatment in each site would produce lower containment of contami-
nants in the nearshore site due to the factors operating on contaminant
mobility and the limited site control relative to upland sites.
Four levels of treatment of slurry, runoff, and leachate water were identified
as follows:
o Level I is the removal by sedimentation of suspended solids and parti-
culate bound contaminants from disposed and site-derived water. This level
would remove 99.9 percent of solids, 80-99 percent of heavy metals, and 50-90
percent of organic contaminants. A representative cost for Level I treatment
of 1,000,000 cubic yards (c.y.) of dredged material at an upland site is $18
million (total project cost, including dredging).
o Level II is additional treatment to remove soluble metals. This level
would increase heavy metals removal to 99 percent. A representative total
project cost for 1 million c.y. at Level II treatment is $19,000»000.
o Level III is treatment to remove soluble organics. This level increases
organics removal to 95 percent. A representative total project cost for 1
million c.y. at level II treatment is $25 million.
o Level IV is final stage treatment to remove dissolved solids. This
level would increase organics removal to 99 percent, but is primarily designed
to remove nonraetallic, inorganic contaminants (e.g., nutrients and common
anions). Of the Level IV treatment systems, distillation is the most expen-
sive, best documented, and best performing process available. A representa-
tive cost for 1 million c.y. treated at level IV is $49 to $79 million.
For Levels I and II treatment methods, the cost of plain sedimentation
represents a major investment relative to chemical clarification, filtration,
and metals precipitation. The addition of these latter treatment methods may
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be relatively cost effective measures of obtaining substantial additional
contaminant removal. Level IV treatment is only a likely consideration for
site runoff and leachate, where the alternative of using an existing municipal
or industrial facility may be available and should be evaluated. Treatment
Levels II-IV require further experience in dredged material applications
before their performance can be fully documented with this medium.
Treatment measures discussed in this report do not involve, with one exception,
the destruction of contaminants. Instead, contaminants are concentrated by
the treatment process. Therefore, treatment designs must account for disposal
of treatment sludges and spent fluids.
For hydraulic dredging, the relative importance of losses at various times and
from various phases during the sediment dredging and disposal process is shown
below, listed in order of decreasing importance:
(1) Short-term loss of sediment and water.
(2) Long-term loss of water.
(3) Short-term loss of volatiles.
(4) Long-term loss of volatiles.
(5) Long-term loss of sediment.
Normally, disposal will result in greater short-term loss of sediment and water
than will dredging. Based on the above ranking of importance, short-term
sedinent and water loss during disposal will be the usual first consideration
and the basis for selecting disposal method and treatment level. Concurrently,
but on a secondary basis, the contribution of dredging to this loss should be
evaluated. The next subsequent step should be selecting appropriate treat-
ment, monitoring, and remedial response to address long-term loss of water-
borne contaminants. Consideration of items (3)—(5) above would depend on
sediment and site-specific conditions.
For mechanical dredging, short-term loss of sediment and water and long-term
loss of water from the disposal site (for upland or nearshore sites) may be
equally important. The proportion of partially soluble contaminants in
disposed sediment that is available for later leaching is increased relative
to that in hydraulically dredged sediments. The amount of sediments and
easily soluble contaminants lost during dredging is also increased relative to
hydraulic dredging. However, the use of watertight buckets may reduce this
loss substantially.
Several open-water, upland, and nearshore sites with high potential of near-
term use for contaminated sediments are recommended for first consideration in
subsequent planning. For open-water sites, further evaluation of the Hylebos/
Browns Point site is recommended because of the potential for more complete
containment of sediments. No further evaluation is recommended for the
Puyallup River delta. For upland sites, Port of Tacoma "D" and the Puyallup
vii
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River/Railroad sites are the most worthy of further evaluation. Their capa-
cities are large, the sites are within pumping distance from a variety of
Commencement Bay dredging sites, and the sites are sufficiently large to
permit onsite treatment facilities to be constructed. For nearsliore sites,
further evaluation of Milwaukee Waterway, the Blair Waterway slips, and the
Blair graving dock sites is recommended. Information needs and recommended
studies identified in this report are summarized below.
o Additional experience and prototype work is needed for several aspects
of aquatic disposal of contaminated sediments. Capping of contaminated sedi-
ments should be demonstrated using equipment, sediments, and material available
in Puget Sound. For nearshore and open-water, confined disposal, experience
in placing underwater clay liners is needed. The vertical diffuser should be
demonstrated in the United States.
o Loss of volatile contaminants through degasser systems on hydraulic
dredges should be investigated. Potential loss should be estimated by obtain-
ing field information on the volume of gas in the sediments in situ. Actual
loss should be studied by monitoring of degasser discharges.
o The availability of special-purpose dredges could be a major consider-
ation in their use in Commencement Bay. Due to the advantages that these
plants offer, specific determinations of their potential availability are
warranted at this stage of planning.
o Additional planning will be needed before the list of potential dis-
posal sites can be pared down to those that are probable for designation. The
generic information needs identified for each type of disposal site should be
pursued as part of ongoing planning in Commencement Bay. In addition, many
site and treatment design requirements can be obtained from sediment tests at
this time.
o Better quantitative prediction of contaminant mobility can be obtained
by conducting pilot-scale laboratory tests to develop empirical relationships
of contaminant mobility under various disposal conditions in combination with
the use of mathematical models to predict this mobility. Tests to measure
long-term contaminant mobility for the three disposal methods and resulting
conditions, and first-stage modeling of mobility, should be considered at this
time.
The broader conclusions and recommendations of this report are provided below:
o The limited disposal capacity, the variable levels and types of sedi-
ment contamination, the multiple locations of dredging, and the anticipated
large volume of contaminated dredged material strongly suggest that any one
solution or one type of disposal site will not suffice for Commencement Bay,
For near-term stages of planning, sites in open water, nearshore, and upland
should all be pursued for potential use. This "mixed" approach will also
allow maximum flexibility in defining appropriate criteria and standards.
o Large, centralized disposal sites and treatment facilities should be
established for use by those with dredging requirements. The site(s) should
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be managed by a single entity and be designed to meet criteria established by
a bay-wide management plan. Conceptually, the high initial cost for acquiring
and developing the disposal site and any associated treatment facilities would
be spread between the dredgers and prorated at an unit cost per each c.y.
disposed. This solution would amortize the expense of initial construction
over time as well as spreading the cost among users; and it would result in
less land being impacted and, therefore, fewer disruptions in land use. Site
monitoring and potential remedial response (mitigation) costs would also be
reduced. Development of a management plan that matches disposal resources to
dredging needs would be a complex and difficult task. For large, volumes of
contaminated material, such as occurs in Commencement Bay, this may be the
only practicable solution.
o Since treatment costs are very expensive, it would be prudent to treat
only those volumes of sediment that meet or exceed the levels that trigger the
need for treatment. This selective dredging and disposal allows maximization
of a limited disposal capacity. However, in order to accomplish this, sedi-
ment characterization may require more samples (at greater cost) than typically
analyzed for many dredging projects. At the same time, this characterization
and subsequent segregation must bear in mind the precision of the dredging
equipment employed.
o Dredging projects involving contaminated materials often encounter
sediments comprised of mostly coarse (sand and gravel), clean material with a
small fraction of fine (silt and mud), contaminated material. Separating
these materials can substantially reduce the volume of contaminated material
that requires special handling and treatment, A separation facility would
take the effluent from a hydraulic slurry and settle out coarse material
first. This material could be removed for use in a number of ways. The
remaining fines are settled into a secondary basin or removed during appro-
priate effluent treatment. The cost of segregation and rehandling may be
compensated for by the reduced cost associated with treating and confining a
lesser volume of contaminated sediment.
o The common theme of dredging, disposal, control, and treatment discus-
sions is the identification of pertinent decisionmaking criteria. These
should define testing methods and interpretation of test results to determine
when certain dredging and disposal options are appropriate and required.
Development of criteria represents the central link between available disposal
sites, the extent and types of sediment contamination, and the navigation and
Superfund needs to move that sediment. The criteria will allow assembly of
the components of a dredging job: type of dredge, disposal site, and treat-
ment levels, and are at the core of a management plan for Commencement Bay.
Therefore, development of criteria should receive primary attention in any
future efforts.
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TABLE OF CONTENTS
Paragraph Page
ACKNOWLEDGEMENTS i
EXECUTIVE SUMMARY ii
TABLE OF CONTENTS xiv
CHAPTER 1.0 INTRODUCTION
1.01 Background 1-1
1.02 Scope of This Report 1-1
1.03 Report Organization 1-2
1.04 Report Assumptions 1-2
1.05 Relation of This Report to Other Work 1-2
1.06 Classification of Commencement Bay Contaminants 1-3
CHAPTER 2.0 DREDGING METHODS AND EQUIPMENT
2.01 Introduction 2-1
2.01.01 Principles of Dredging 2-1
2.01.02 Types of Dredges 2-2
2.01.03 Dredging Techniques Not Evaluated in This Report 2-3
2.02 Hydraulic Dredges 2-3
2.02.01 Pipeline Cutterhead Dredges 2-4
a. Description of Equipment 2-4
b. Description of Operation 2-9
c. Characteristics 2-11
d. Equipment and Operational Considerations 2-11
e. Operational Controls 2-11
f. Dredge Modifications 2-13
2.02.02 Suction and Dustpan Dredges 2-15
a. Description of Equipment 2-15
b. Description of Operation 2-15
c. Characteristics 2-15
d. Equipment and Operational Considerations 2-18
e. Operational Control and Dredge Modifications 2-18
2.02.03 Hopper Dredges 2-18
a. Description of Equipment 2-18
b. Description of Operation 2-18
c. Characteristics 2-21
d. Equipment and Operational Considerations 2-21
e. Operational Control 2-21
2.02.04 Special-Purpose Dredges 2-22
a. Mudcat Dredge 2-22
b. Pneuma Pump 2-22
c. Oozer Dredge 2-26
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TABLE OF CONTENTS (con.)
Paragraph Page
d. Cleanup System 2-26
e. Refresher System 2-26
f. Availability of Cleanup, Oozer, and
Refresher Dredges 2-26
2.03 Mechanical Dredges 2-29
a. Description of Equipment 2-29
b. Description of Operation 2-29
c. Characteristics 2-29
d. Equipment and Operational Considerations 2-31
e. Operational Control and Modification 2-31
f. Dredge Modifications 2-31
2.04 Contaminant Efficiency of Dredging Methods 2-32
2.04.01 Volatile Phase Contaminants 2-32
a. General 2-32
b. Hydraulic Dredging 2-33
c. Mechanical Dredging 2-34
2.04.02 Soluble Phase Contaminants 2-34
a. General 2-34
b. Hydraulic Dredging 2-34
c. Mechanical Dredging 2-34
2.04.03 Sediment-Bound Contaminants 2-35
CHAPTER 3.0 DISPOSAL METHODS AND SITES
3.01 Introduction 3-1
3.02 Transportation and Discharges from Various
Types of Dredges 3-1
a. Hopper Dredge 3-2
b. Mechanical Dredge 3-2
c. Cutterhead Pipeline Dredge 3-3
3.03 Disposal Methods 3-4
3.03.01 Open-Water Disposal 3-4
a. General Site Criteria 3-6
b. General Designs 3-7
(1) Deep-water Mound 3-7
(2) Deep-water Confined 3-12
(3) Shallow-water Confined 3-12
(4) Waterway Confined 3-12
3.03.02 Upland Disposal 3-13
a. General Site Criteria 3-13
b. General Designs 3-17
3.03.03 Nearshore Disposal 3-17
3.04 Contaminant Efficiency of Disposal Methods 3-17
3.04.01 General 3-17
xi
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TABLE OF CONTENTS (con.)
Paragraph Page
3.04.02 Volatile Phase Contaminants 3-19
a. Open-Water Disposal 3-20
b. Upland Disposal 3-20
c. Nearshore Disposal 3-20
3.04.03 Soluble Phase Contaminants 3-20
a. Open-Water Disposal 3-21
b. Upland Disposal 3-22
c. Nearshore Disposal 3-22
3.04.04 Sediment-Bound Contaminants 3-23
a. Open-Water Disposal 3-23
b. Upland Disposal 3-23
c. Nearshore Disposal 3-23
3.05 Disposal Sites 3-23
3.05.01 Site Selection Criteria 3-24
3.05.02 Open-Water Disposal Sites 3-25
a. Puyallup River Delta Disposal Site 3-25
(1) Description 3-25
(2) Limitations 3-26
(3) Information Needs 3-26
b. Department of Natural Resources Disposal Site 3-26
(1) Description 3-26
(2) Limitations 3-26
(3) Information Needs 3-26
c. Hylebos/Browns Point Disposal Site 3-26
(1) Description 3-26
(2) Limitations 3-28
(3) Information Needs 3-28
3.05.03 Upland Sites 3-28
a. Puyallup Mitigation Site 3-28
(1) Description 3-28
(2) Limitations 3-29
(3) Information Needs 3-29
b. Port of Tacoma Site "D" 3-29
(1) Description 3-29
(2) Limitations 3-29
(3) Information Needs 3-29
c. Puyallup River/Railroad Site 3-29
(1) Description 3-29
(2) Limitations 3-31
(3) Information Needs 3-31
d. Port of Tacoma Site "E" 3-31
(1) Description 3-31
(2) Limitations 3-31
(3) Information Needs 3-31
e. Hylebos Creek Sites Nos. 1 and 2 3-31
(1) Description 3-31
(2) Limitations 3-32
(3) Information Needs 3-32
xii
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TABLE OF CONTENTS (con.)
Paragraph
3.05.04
Page
Nearshore Sites
3-32
a. Middle Waterway !
Bite
3-32
(1) Description
3-32
(2) Limitations
3-34
(3) Information
Needs
3-34
b. Milwaukee Waterway Site
3-34
(1) Description
3-34
(2) Limitations
3-34
(3) Information
Needs
3-34
c. Blair Waterway Slips
3-34
(1) Description
3-34
(2) Limitations
3-35
(3) Information
Needs
3-35
d. Blair Graving Dock
3-35
(1) Description
3-35
(2) Limitations
3-35
(3) Information
Needs
3-35
e. Hylebos Waterway
No. 1
3-35
(1) Description
3-35
(2) Limitations
3-36
(3) Information
Needs
3-36
f. Hylebos Waterway
No. 2
3-36
(1) Description
3-36
(2) Limitations
3-36
(3) Information
Needs
3-36
Off-site Options
3-36
3.05.05
CHAPTER 4.0 SITE CONTROL AND TREATMENT PRACTICES
4.01 Introduction 4-1
4.02 Site Controls for Disposal 4-1
4.02.01 Overview 4-1
4.02.02 Controls for Open-Water Disposal 4-1
a. Capping Materials 4-3
b. Stability of Capping Materials 4-4
4.02.03 Controls for Upland and Nearshore Disposal 4-5
a. Background 4-5
b. Liners 4-5
(1) Soil Liners 4-5
(2) Flexible Membrane Liners 4-7
(3) Limitations 4-8
c. Covers and Run On Control 4-8
(1) Cover Types 4-8
(2) Limitations 4-9
xiii
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TABLE OF CONTENTS (con.)
Paragraph Page
d. Underdrains 4-9
(1) Gravity Underdrainage 4-9
(2) Vacuum Assisted Underdrainage 4-9
(3) Limitations 4-11
e. Stabilization of Sediment 4-11
(1) Lime-Treated Sediment 4-11
(2) Dust Pallatives 4-11
(3) Water Sprinkling 4-13
(4) Limitations 4-13
f. Biological Decontamination 4-13
4.03 Treatment for Nearshore and Upland Disposal Sites 4-13
4.03.01 Introduction 4-13
4.03.02 Plain Sedimentation 4-17
a. Overview 4-17
b. Contaminant Removal by Plain Sedimentation 4-17
4.03.03 Chemical Clarification 4-17
a. Applicability 4-17
b. Limitations 4-18
c. Removal Efficiency 4-18
4.03.04 Filtration 4-18
a. Pervious Dikes 4-18
b. Sandfill Weirs 4-18
c. Limitations 4-18
(1) Pervious Dikes 4-18
(2) Sandfill Weirs 4-22
d. Removal Efficiency 4-22
4.03.05 Chemical Precipitation 4-22
a. Applicability 4-22
b. Limitations 4-22
c. Removal Efficiency 4-22
4.03.06 Carbon Adsorption 4-22
a. Overview 4-22
b. Carbon Columns 4-25
c. Powdered Carbon 4-25
d. System Configuration and Efficiencies 4-25
e. Carbon Regeneration 4-25
f. Limitations 4-29
4.03.07 Ozonation 4-29
a. Overview 4-29
b. Effectiveness 4-30
c. Limitations 4-30
4.03.08 Dissolved Solids Removal Systems 4-30
a. Overview 4-30
b. Distillation 4-31
c. Electrodialysis 4-31
d. Reverse Osmosis 4-32
xiv
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TABLE OF CONTENTS (con.)
Paragraph Page
e. Effectiveness 4-32
(1) Distillation 4-32
(2) Electrodialysis 4-32
(3) Reverse Osmosis 4-32
f. Limitations 4-32
(1) Distillation 4-32
(2) Electrodialysis 4-32
(3) Reverse Osmosis 4-33
4.03.09 Sripping 4-33
a. Overview 4-33
b. Effectiveness 4-33
c. Limitations 4-36
4.03.10 Ion Exchange 4-36
a. Overview 4-36
b. Effectiveness 4-36
c. Limitations 4-36
4.04 Runoff and Leachate Treatment 4-37
4.04.01 Overview 4-37
4.04.02 Treatment of Landfill Leachate 4-37
a. Biological Treatment 4-38
b. Physical-Chemical Treatment 4-38
4.05 Disposition of Treatment Materials 4-38
4.06 Biological Control of Disposal Areas 4-39
4.06.01 Overview 4-39
4.06.02 Biological Control Measures 4-40
4.07 Monitoring and Remedial Response 4-40
4.07.01 Purpose and Need 4-40
4.07.02 Monitoring Parameters and Frequency 4-40
a. Open-Water 4-40
b. Upland 4-41
c. Nearshore 4-41
4.07.03 Remedial Response 4-41
a. Open-Water 4-41
b. Upland 4-41
c. Nearshore 4-43
CHAPTER 5.0 COSTS OF DREDGING, DISPOSAL, CONTROL AND TREATMENT
5.01 Introduction 5-1
5.02 Dredging Costs 5-1
5.02.01 General Cost Principles 5-1
5.02.02 Hydraulic Dredges 5-1
a. Cutterhead 5-1
b. Suction and Dustpan 5-10
c. Hopper 5-10
d. Special Purpose 5-10
xv
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TABLE OF CONTENTS (con.)
Paragraph
Page
5.02.03
Mechanical Dredges
5-10
5.03
Disposal Costs
5-10
5.03.01
General Cost Principles
5-10
5.03.02
Open-water Disposal
5-11
a. Deep-water Mound
5-11
b. Deep-water Confined
5-12
5.03.03
Upland Disposal
5-12
5.03.04
Nearshore Disposal
5-12
5.03.0 5
Off-site Disposal
5-13
5.03.06
Potential Disposal Site Costs
5-13
a. Puyallup River Delta Site
5-13
b. Department of Natural Resources Site
5-13
c. Hylebos/Browns Point Site
5-13
d. Puyallup Mitigation Site
5-13
e. Port of Tacoma Site "D"
5-13
f. Puyallup River/Rai Iroad Site
5-14
g. Port of Tacoma Site "E"
5-14
h. Hylebos Creek Sites Nos. 1 and 2
5-14
i. Middle Waterway Site
5-14
j. Milwaukee Waterway Site
5-14
k. Blair Waterway Slips
5-14
1. Blair Graving Dock Site
5-14
m. Hylebos Waterway No. 1
5-14
n. Hylebos Waterway No. 2
5-14
5.04
Control and Treatment Costs
5-15
5.04.01
Control and Treatment Cost Principles
5-15
5.04.02
Nearshore vs. Upland Treatment Costs
5-15
5.05
Other Cost Factors
5-17
CHAPTER 6.0 DISCUSSION AND CONCLUSIONS
6.01
Introduct ion
6-1
6.02
Dredging Methods
6-1
6.02.01
Genera I
6-1
6.02.02
Selection of a Dredge Type
6-4
6.03
Disposal Methods
6-4
6.04
Site Control and Treatment Methods
6-8
6.05
Relative Containment During Dredging, Disposal,
Control, and Treatment
6-8
6.06
Disposal Sites
6-12
6.07
Information Needs and Recommended Study
6-17
CHAPTER 7.0 REFERENCES
7-1
xv i
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TABLE OF CONTENTS (con.)
APPENDIXES
Number Page
1 A Solubility and Mobility Classification of
Organic Chemicals Identified in Commencement
Bay Sediments, 1983. Waterways Experiment
Station, U.S. Army Corps of Engineers,
Vicksburg, Mississippi
2 Letter Reports on Long-Term Mobility of Sediment
Contaminants Under Various Disposal Conditions
a. Dr. Louis Thibodeaux, University of Arkansas
b. Dr. Paul Roberts, Stanford University
3 Treatment Calculations
FIGURES
2-1 Typical Components of a Pipeline Cutterhead
Dredge 2-5
2-2 Cross Section View of Typical Cutterhead and
Suction 2-8
2-3 Operation of a Cutterhead Dredge (plan view) 2-10
2-4 Walking Spud 2-14
2-5 Plain Suction Dredge 2-16
2-6 Dustpan Dredge 2-17
2-7 Typical Hopper Dredge Components 2-19
2-8 Hopper Dredge California Draghead 2-20
2-9 Mudcat Dredge 2-23
2-10 Operating Cycle of the Pneuraa Pump 2-24
2-11 Cleanup System Dredgehead 2-27
2-12 Refresher System 2-28
2-13 Bucket Dredge 2-30
3-1 Ocean Disposal of Dredged Material from Hopper
Dredge 3-3
3-2 Submerged Diffuser System with Discharge Barge 3-5
3-3 Submerged Diffuser (Highlight) 3-6
3-4 Deepwater Mound 3-8
3-5 Deepwater Confined 3-9
3-6 Shallow Water Confined 3-10
3-7 Waterway Confined 3-11
3-8 Upland Disposal Site 3-14
3-9 Conceptual Design of Confined Dredged Material
Disposal Area 3-15
3-10 Examples of Longitudinal and Transverse Spur Dike
Configurations 3-16
3-11 Nearshore Disposal Sites 3-18
3-12 Open-Water Disposal Sites 3-27
xv ii
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TABLE OF CONTENTS (con.)
Number page
FIGURES (con.)
3-13 Upland Disposal Sites 3-30
3-14 Nearshore Disposal Sites 3-33
4-1 Capping with Submerged Diffuser 4-2
4-2 Examples of Surface Cover Systems 4-10
4-3 Schematic of Chemical Clarification Facility 4-19
4-4 Pervious Dikes 4-26
4-5 Sandfill Weirs 4-21
4-6 Granular Activated Carbon System Configuration 4-26
4-7 Air Stripping Towers 4-34
4-8 Typical Steam Stripping System 4-35
4-9 Upland Site Well Monitoring System - Plan View 4-42
TABLES
2-1 Typical Specifications for Five Sizes of
Pipeline Dredges 2-9
2-2 Specifications for Typical Cutterhead Dredges
Working in Commencement Bay 2-12
2-3 Suspended Sediment Levels Produced by Various
Special-Purpose Dredges 2-25
3-1 Initial Site Selection Criteria 3-24
4-1 Summary of Liner Types 4-6
4-2 Primary Function of Cover Layers 4-9
4-3 Listing of Water Treatment Processes 4-15
4-4 Contaminant Removal Efficiency of Water Treatment Levels 4-16
4-5 Removal of Heavy Metals by Lime Coagulation
and Recarbonation 4-23
4-6 Properties of Several Commercially Available
Carbons 4-24
4-7 Contacting Systems _ 4-27
4-8 Potential for Removal of Inorganic Material by
Activated Carbon 4-28
5-1 Cost Factors Checklist 5-2
5-2 Typical Dredge Characteristics and Costs 5-3
5-3 Cost of Disposal and Control Options for Handling
Contaminated Sediments 5-4
5-4 Disposal Site Preparation Costs 5-5
5-5 Representative Costs for Synethic Liners 5-6
5-6 Unit Costs for Soil Liner and Surface Cover Materials 5-7
5-7 Treatment Level Costs Comparison for Nearshore Site 5-8
5-8 Treatment Level Costs Comparison for Upland Site 5-9
6-1 Summary of Dredge Operating Characteristics 6-2
6-2 Comparison of Disposal Method Effectiveness 6-5
6-3 Applicability and Potential Use of Various Control
and Treatment Alternatives for Contaminated
Sediments in Commencement Bay 6-9
xviii
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TABLE OF CONTENTS (con.)
Number Page
TABLES (con.)
6-4 Case Study Sediment Chemistry 6-13
6-5 Representative and Range of Values for Soluble and
Easily Solubilized Metals 6-15
6-6 Case Study Partitioning Values 6-16
6-7 Partitioning Coefficients for Organic Contaminants 6-17
6-8 Evaluation of Open-Water Disposal Sites 6-21
6-9 Evaluation of Upland Disposal Sites 6-22
6-10 Evaluation of Nearshore Disposal Sites 6-24
PHOTOGRAPHS
2-1 Forward Components of a Pipeline Cutterhead Dredge 2-6
2-2 Pipeline Cutterhead Dredge Spud Gantry 2-7
2-3 Closed Nose Basket Cutter 2-8
2-4 Hopper Dredge California Draghead 2-20
PLATES
Plate 1 Site Boundaries of the Commencement Bay Nearhore/
Tideflats Superfund Site
Plate 2 Potential Disposal Sites in Commencement Bay,
Washington
Plate 3 Water Treatment Processes Flow Diagram
xix
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CHAPTER 1.0 INTRODUCTION
1.01 Background. The State of Washington Department of Ecology (WDOE) has
entered into a cooperative agreement with the U.S. Environmental Protection
Agency (EPA) to act as lead agency in the implementation of Phase I Remedial
Investigations for the Commencement Bay Nearshore/Tideflats Superfund Site,
Washington. Superfund remedial action may involve removal and handling of
contaminated sediments found in the bay. In addition, ongoing and proposed
navigation activities in the nearshore areas of Commencement Bay may require
dredging and disposal of contaminated sediments. As a result, Superfund site
investigations and planning of navigation projects require identification and
evaluation of alternative methods for dredging and disposal of contaminated
sediments. By agreement with WDOE, the Seattle District, U.S. Army Corps of
Engineers, conducted an analysis of alternative dredging and disposal methods
with potential application to Commencement Bay. This draft report contains
the alternatives analysis.
1.02 Scope of This Report. The Commencement Bay Nearshore/Tideflats Superfund
Site includes portions of the communities of Ruston and Tacoma, the western
shoreline of the bay, and the land and nearshore water areas around the various
waterways of the bay (plate 1). While the boundaries of the site may change
as new information becomes available, the waterward limit of the site is
presently defined as the water depth contour at -60 feet mean lower low water
(MLLW).
This report describes and evaluates alternative dredging methods and equip-
ment, disposal methods and sites, and site control and treatment practices for
contaminated sediments derived from Commencement Bay. These alternatives are
evaluated based on the following factors:
o Cost of each alternative.
o Degree of contaminant confinement and release resulting with each
alternative .
o Considerations and limitations specific to each alternative (e.g.,
equipment and site availability, method efficiency, equipment depth limita-
tions, sociopolitical concerns, and other indicators of practicability).
This report solely addresses contaminant removal from those portions of the
Superfund site that are under water (intertidal and subtidal to -60 feet
MLLW). Removal of contaminated soil or materials from upland areas is not
addressed. The remedial technologies discussed in this report pertain to
dredging and disposal, including capping, of contaminated sediment that has
been dredged and relocated. In-place remedial actions, such as placement of
barriers to block underwater contaminant seeps into the waterways or capping
of contaminated materials in situ under water, are not addressed.
1-1
-------
1.03 Report Organization. Dredging techniques and technology are discussed
in chapter 2. Disposal methods and sites are discussed in chapter 3. Possi-
ble treatment methods for contaminated sediments and water are discussed in
chapter 4. The costs of dredging, disposal, and treatment alternatives are
presented and summarized in chapter 5. Chapter 6 summarizes the relationships
between the alternatives and presents those conclusions that can be formulated
at this stage of planning for Commencement Bay.
1.04 Report Assumptions. The following assumptions underlie the evaluation
of alternatives discussed in this report.
o The physical characteristics (e.g., grain size) of the sediment to be
dredged are within the range typically reported for the Commencement Bay
nearshore area.
o The sediment to be dredged is not classifiable as "dangerous" or
"extremely hazardous" pursuant to the Resource Conservation and Recovery Act
(RCRA) or the State of Washington Dangerous Waste Regulations.
o The sediment to be dredged is not acceptable for unconfined, open-water
disposal due to the presence of contamination exceeding criteria. These
criteria are considered to be presently unspecified (although WDOE has estab-
lished interim guidelines for consideration).
o In the absence of specific sediment contamination criteria, the removal
and handling of contaminated sediments is evaluated in terms of maximum con-
finement and minimum release or redistribution of contaminants.
o For purposes of discussion in this report, contaminants are loosely
classified as volatile, soluble, or sediment-bound. Contaminant evaluations
are based on these classifications.
o Cost analysis of alternatives is based on an "order-of-magnitude"
precision using costs incurred on similar projects, estimates of costs associ-
ated with implementing a typical dredging project, and/or relative cost
values. Due to the number of factors that influence cost, ranges of cost are
occasionally presented. However, attempt has been made to relate cost
principles to specific Commencement Bay considerations.
1.05 Relation of This Report to Other Work. For the Commencement Bay
Nearshore/Tideflats Superfund Site, this report constitutes an evaluation of
potential remedial technologies for clean-up of contaminated sediments. As
part of the remedial investigations, the WDOE is conducting a separate study
to define the extent of contamination at the site. A central component of the
study includes development of decision criteria for identifying "problem"
sediments that are sufficiently hazardous in place to warrant removal. This
report addresses options for removal and disposal of these sediments.
While generally effective methods can be identified, specific recommendations
for dredging, disposal, and site control methods are difficult to make without
first defining the criteria that need to be met or without having some project
1-2
-------
specific information (e.g., location, quantity of dredged material, size of
disposal site). Therefore, the basic intent of this report is to display and
evaluate alternatives that should be considered in selecting appropriate
dredging and disposal methods once criteria are available. Moreover, this
display of alternatives can assist in establishing criteria that are techni-
cally feasible and for which the cost of meeting specific criteria has been
cons idered.
As a related task, the Corps of Engineers is developing a decisionmaking
framework for disposal of contaminated sediments derived from Commencement
Bay. The framework is being prepared by the Corps' Waterways Experiment
Station (WES), under agreement with the Seattle District and WDOE. It will
specify testing requirements and methods to evaluate sediment contamination,
and will define test result interpretation to determine when various disposal
controls and restrictions (described in this re port) are required.
1.06 Classification of Commencement Bay Contaminants. As mentioned above,
this report addresses contaminant confinement and release during dredging and
disposal in terms of three generalized contaminant classes: volatile,
soluble, and sediment-bound. These classes generally refer to the phase (gas,
liquid, solid) for which a contaminant has a relatively greater affinity and
in which higher concentrations might be expected during the dredging and dis-
posal process. This classification is done in full recognition that contami-
nants will partition and move between these phases to differing extents based
on a number of factors (appendix 1). The factors that govern contaminant
partitioning, mobility, and consequent loss during dredging and disposal are
discussed briefly in the following chapters and in appendix 2 of this report.
Contaminant specific information is unavailable for many contaminants and
dredging disposal methods. Additionally, site-specific conditions will
influence the amount of a contaminant found in any one phase. Therefore, no
specific list of contaminants is identified for each class, and the classifi-
cation is used solely as a basis for comparing dredging and disposal alterna-
tives based on existing data and information. Appendix 1 provides a ranking
of certain organic contaminants found in Commencement Bay in terms of their
relative tendency to move from sediment-bound to soluble or volatile phases.
Chapter 6 illustrates application of partitioning concepts to a case study
from Commencement Bay.
1-3
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CHAPTER 2.0 DREDGING METHODS AND EQUIPMENT
2.01 Introduction. This chapter describes dredging methods and equipment and
evaluates them in terms of availability, production rates, and contaminant
containment during use. Characteristics, operational considerations and con-
trol, and equipment considerations and modifications for dredging contaminated
sediments are described for each dredging alternative. Costs of dredging
alternatives are summarized in chapter 5.
2.01.01 Principles of Dredging. Dredging equipment and methods have been
developed over the years to enhance one of the two basic uses of dredging:
a. Underwater excavation to provide or maintain navigable water depths in
harbors and channels.
b. Underwater mining and sand and gravel production.
The dredging process itself involves four basic tasks: (1) the loosening or
dislodging of sediment by mechanically penetrating, grabbing, raking, cutting,
drilling, blasting, or hydraulically scouring; (2) a lifting action accom-
plished by mechanical devices such as buckets or by hydraulic suction; (3) the
transporting of dredged material by pipelines, scows, hopper dredges, or
trucks; and (4) disposing of the material by either discharging from a pipe-
line or by dumping from trucks into a confined disposal area, bottom dumping
from barges, or pumping out of scows or hoppers. In some hydraulic operations
all four actions are carried out continuously and concurrently by a single
piece of equipment, but in others the various functions are performed sepa-
rately and intermittently, utilizing two or more pieces of equipment. For
instance, where dredging equipment does not have on-board storage capability
or where environmental considerations preclude the possibility of disposing of
the material into open water adjacent to the dredging site, auxiliary equip-
ment (scows or barges) is required for storage and transport of the dredged
material.
Dredging practices in the United States have evolved to achieve the greatest
possible economic returns through maximizing production with only secondary
consideration given to environmental or esthetic impacts. The type of equip-
ment and methods used in a given job traditionally have been based on the
following very practical considerations:
o Amount of sediment to be dredged.
o Physical characteristics of the dredged material.
o Water depths and hydrologic characteristics.
o Dredged material disposal considerations (type and location of sites).
o Availability of dredging equipment.
2-1
-------
Dredging of contaminated sediments requires the additional consideration of
contaminant loss during the extraction process and meeting of applicable
criteria pertaining to removal efficiencies and/or environmental protection.
For most jobs, the controlling factors in equipment selection are the degree
of contaminant confinement required and the cost necessary to achieve this
confinement. For any given dredging method, technologies and practices exist
that increase contaminant removal and confinement, though confinement effi-
ciencies will vary greatly between techniques. Therefore, the critical
element in the selection of a dredging technique is the definition of criteria
that are to be met. These criteria may specify removal efficiencies, allow-
able losses, emission rates, and/or concentrations for individual contaminants,
allowing a variety of dredging techniques to be considered, or the criteria
may specify certain equipment or method as requisite for given levels and
types of contamination. Other than through exercise of judgment, recommended
techniques are difficult to determine prior to consideration of these criteria.
Many operational modifications and controls that can be used for working in
contaminated sediments are not standard or accepted practices. Therefore,
contractors bidding on a job requiring these modifications may feel the need
to protect their job profits by increasing bids. A solution to this cost
escalation effect is hourly rental rates until the operators gain experience
in use of a specific control practice. Better cost control can result with
this approach.
The principles and specifics of dredging costs are discussed in chapter 5,
except where cost information is used in demonstrating calculations of
dredging productivity.
2.01.02 Types of Dredges. Dredging equipment and its nomenclature resist
precise categorization. As a result of specialization and tradition in the
industry, numerous descriptive, often overlapping, terms categorizing dredges
have developed. For example, dredges can be classified according to: the
basic means of moving material (mechanical or hydraulic); the method of
storage or disposition of dredged material (pipeline or hopper); the device
used for excavating sediments (cutterhead, dustpan, plain suction); the type
of pumping device used (centrifugal, pneumatic, or airlift); and others.
Two basic types of dredges, hydraulic and mechanical, are addressed in this
report. These descriptive categories were selected based on the differences
each have in terms of contaminant loss during dredging.
Mechanical dredges remove bottom sediment through the direct application of
mechanical force to dislodge and excavate the material at almost in situ
densities. Clamshell, dipper, dragline, and ladder dredges are types of
mechanical dredges.
Hydraulic dredges remove and transport sediment in liquid slurry form. They
are usually barge mounted and carry diesel or electric powered centrifugal
pumps with discharge pipes ranging from 6 to 48 inches in diameter. Cutter-
head, suction, dustpan, hopper, and "special-purpose" dredges are types of
2-2
-------
hydraulic dredges. "Special-purpose" dredges, for this report, are dredges
designed to pump high solids concentrations and/or produce low turbidity
leveIs.
2.01.03 Dredging Techniques Not Evaluated in This Report. Because this
report focuses on dredge applications to removal of contaminated sediments,
the evaluation focuses on maximizing contaminant and solids removal and con-
tainment, cost and production rates, and equipment availability. Dredge types,
operational practices and equipment modifications that produce relatively high
suspended solids concentrations at the extraction site in the water column,
and high or additional costs without distinct advantages, are not evaluated in
this report. These alternatives and the reasons for excluding them are
briefly described below.
Agitation dredging is the process of suspending bottom sediments in the water
column and allowing currents to carry them from the project area. Because of
the assumption that material to be dredged is unacceptable for unconfined,
open-water disposal, this dredging technique is not included for evaluation.
For the same reason, sidecasting disposal of dredged sediment is not
considered.
The orange-peel dredge is a mechanical dredge with a modified bucket. The
bucket consists of four moving parts (as opposed to two for the clamshell
bucket) and is designed primarily for handling rock. The orange-peel dredge
results in higher loss of water and sediment during dredging and lacks any
distinct advantage over the more common clamshell bucket.
The bucket ladder dredge is a mechanical dredge that utilizes an endless chain
of buckets that loop around two, structurally-held tumblers. Developed pri-
marily for mining and handling of coarse material, this dredge has very limited
and diminishing availability, a high first cost, and produces high suspended
solids concentrations in the water column during extraction.
Dragline dredges are shore-mounted, mechanical dredges that use a bucket and
wire rope to pull or drag sediment along the bottom. This technique produces
high suspended solids concentrations during dredging and only average removal
e fficiencies.
Dipper and backhoe dredges are mechanical dredges with a ladder and bucket
operated by hydraulic cylinders. Their production rates are similar to other
mechanical dredges, but they produce relatively high levels of suspended
solids in the water column and are more expensive to use.
The Japanese have developed a submerged discharge system for overflow from
hopper dredges known as the antiturbidity overflow system (ATOS). ATOS was
developed to reduce surface turbidity in receiving waters by discharging the
overflow directly into subsurface waters, but this system does not reduce
overall resuspension of sediment.
2.02 Hydraulic Dredges. All hydraulic dredges have one thing in common; they
use a pipeline to move the slurried dredged materials. A pump supplies the
2-3
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force to transport the slurry (dredged materials and water) through a pipeline
from the channel bottom to the discharge point. Hydraulic dredges can dis-
charge the dredged materials into a hopper or bin on the dredge itself, into
barges tied alongside or pump the dredged material long distances (up to 2
miles) to open-water, nearshore, or upland disposal sites.
2.02.01 Pipeline Cutterhead Dredges. The most common type of dredge used in
the United States and the Pacific Northwest today is the pipeline cutterhead
dredge. Because of its high potential for use in Commencement Bay, and
because it is the basic dredge type to which many of the contaminant related
modifications have been applied, a detailed explanation of this type of dredge
and its components is given. It has the advantage of being able to excavate
materials, move them hydraulically, and dispose of them without rehandling.
These dredges are generally classified by size in accordance with the diameter
of the discharge pipeline: small class pipeline dredges have a 4-inch to
14-inch discharge; medium class pipeline dredges have a 16-inch to 22-inch
discharge; and large class pipeline dredges have a 24-inch to 36-inch dis-
charge. Typical specifications for five sizes of pipeline dredges are shown
in table 2-1.
a. Description of Equipment. Figure 2-1 shows the major components of a
pipeline cutterhead dredge. These components consist of a cutterhead on the
end of a suction pipeline, a ladder structure supporting the suction pipeline
and cutterhead, support frames (A and H) for the ladder, hoisting equipment,
main pump and main engine, the spud and support gantry, and a floating dis-
charge pipeline. Photographs 2-1 and 2-2 show the forward components of the
cutterhead dredge and the spud gantry, respectively.
o Cutterhead. The cutterhead is the most forward component of the
dredge. It is basket shaped, with spiral blades forming the sides of the
baskets as shown in figure 2-2 and photograph 2-3. It rotates slowly at a
speed of 5 to 30 revolutions per minute (r.p.m.) while the blades loosen
materials to be dredged.
A secondary purpose of the cutter is to prevent large debris from entering or
plugging the intake pipe. Cutter diameters vary from less than 2 feet for a
small dredge and up to 10 feet for a large dredge. The many types of cutter-
heads and modifications to cutters allow efficient dredging of all type9 of
materials. Pick-type teeth can be added to facilitate dredging in hard packed
materials, coral, and soft rock.
o Ladder and Suction. The ladder is a heavy triangular steel frame
extending forward from the hull. The dredge cutter is attached to the forward
end of the ladder. Winch gear attached to the A frame raises or lowers the
cutter end of the ladder. The suction pipe runs from the center of the
cutterhead through the ladder to the dredge pump. Suction diameters are
usually equal to or slightly larger than the dredge discharge pipeline
diameter.
2-4
-------
GANTRY
LEVER
ROOM
FLOATING LINE
MAIN PUMP. H0,ST
r 1—J
PONTOON
SPUD
DREDGED BOTTOM
HULL
SUCTION
H FRAME
A FRAME
CUTTER
MOTOR
MAIN
ENGINE
LADDER
CUTTER
Figure 2-1: Typical Components ol Pipeline Cutterhead Dredge
2-5
-------
*
H FRAMI
LADDER
PUMPflf
LADDI
A FRAME
Photograph 2-1: Forward Components of a Pipeline Cutterhead Dredge
2-6
-------
SPUD
GANTRY
dredge
SPUD —
Photograph 2-2: Pipeline Cutterhead Dredge Spud Gantry
2-7
-------
Photograph 2-3: Closed Nose Basket Cutter
LADDER HEAD
CUTTER
LOOSE
MATERIAL
LADDER
SUCTION
CUTTER
SHAFT
VARIES WITH SIZE
OF CUTTER. APPROX.
0.7 x LENGTH OF
CUTTER AT
MAXIMUM DEPTH
DREDGED
BOTTOM
Figure 2-2: Cross-Section View of Typical Cutterhead and Suction
2-8
-------
TABLE 2-1
TYPICAL SPECIFICATIONS FOR FIVE SIZES OF PIPELINE DREDGES
(HUSTON, et al., 1976)
Size of Discharge Pipe, In Inches
Item
12
16
20
24
28
Length, in feet
100
120
140
160
175
Beam, in feet
35
40
45
50
50
Depth, in feet
8
9
10
12
15
Displacement, in tons
560
840
1,200
1,850
3 ,000
Pump Power, in brake
horsepower
570
1,000
1,500
2,700
5,000
Pump Speed, in revolutions
per minute
500
400
350
325
300
Cutter Power, in brake
horsepower
150
200
400
750
1,000
Cutter Speed, in revolutions
per minute
5-30
5-30
5-30
5-30
5-30
Spud Length, in feet
55
60
70
90
100
Ladder Length, in feet
50
55
60
70
80
Maximum Pipeline, in feet
2 ,500
4,000
5 ,000
7 ,000
9 ,000
Maximum Width of Cut, in feet
160
200
220
2 70
325
Minimum Width of Cut, in feet
50
60
70
90
90
Maximum Digging Depth, in feet
35
40
45
50
60
Minimum Digging Depth, in feet
4
5
6
8
12
o Main Pump. The main dredge pump is located forward in the hull of the
dredge at the lowest possible elevation. This low elevation reduces the
distance the dredge must lift the slurry under vacuum conditions. The dredge
pump has a height of approximately four times the discharge pipe diameter and
a vaned impeller rotating between 250 r.p.m.'s (for small dredges) to 900
r.p.m.'s (for large dredges). The rotating vaned impeller centrifugally
forces the dredged slurry to the outer circumference of the dredge pump shell
where it enters the discharge line at pressures of 50 to 300 pounds per square
inch (psi).
b. Description of Operation. The cutterhead dredge.is generally equipped
with two stern spuds that hold the dredge in working position and help to
advance the dredge into the cut or excavating area. During operation, the
cutterhead dredge swings alternately from side to side using the port and
starboard as a pivot (figure 2-3). Cables attached to anchors on each side of
the dredge control lateral movement.
Excavated material is pumped through the discharge pipe to the disposal site.
Open-water disposal requires only a floating discharge pipeline made up of
2-9
-------
CUTTERHEAD
ANCHOR
ANCHOR
DREDGE
BO
(UP)B" ,{a o (DOWN)
SPUDS
I
Figure 2-3: Operation of Cutterhead Dredge — Plan View
2-10
-------
sections of pipe mounted on pontoons and held in place by anchors. Additional
sections of shore pipeline are required when upland disposal is used. The
excavated materials may be placed in hopper barges for disposal in open water
or in confined areas that are remote from the dredging site. Depending on the
size of the dredge and the physical character of the material, pipeline trans-
port distances can range up to about 2 miles. Transportation beyond that
point usually requires another pump to "boost" the slurry along. Distances
less than 2 miles may require booster pumps for coarse sediments, with small
dredges, and to dispose in sites that are elevated in relation to the dredge
(1 foot of vertical discharge pumping is approximately equal to 200 feet of
horizontal pumping distance).
c. Characteristics. Cutterhead dredges in pipeline diameters from 8
inches through 27 inches are readily available in the Pacific Northwest.
Table 2-2 shows specifications for typical cutterhead dredges. The minimum
depth of single pass excavation would be approximately the same as one-half
the pipeline diameter. Production (Prod.) for minimum depth pass excavation
can be calculated from the table as follows:
, . . (1/2 x Discharge Diameter) . N
Prod. (Mm. Pass) = 7——: r——r* - —>. x Prod. (Max. Pass)
(Maximum Depth Pass Excavation)
Actual vertical precision of the cut is often limited by the mechanical
control of the ladder and suction head to approximately 1 foot.
d. Equipment and Opcrationa 1 Considerations. Cutterhead dredges can
excavate all anticipated Commencement Bay materials (except where old piers
and piling may be encountered) and pump the dredged materials through pipe-
lines to an upland, nearshore, or open-water disposal site without rehandling.
This mimimizes handling of, and exposure to, contaminated dredged material.
Most available cutterhead dredges have Limited capacity for dredging deeper
than 50 feet below water level. Dredge ladder modifications would be required
to dredge in deeper water. Conventional cutterhead dredges are not self
propelled but require towboats to move them between dredging locations. Thus,
mobilization and set up are major and costly undertakings.
e. Operational Controls. There are a number of operator and operational
controls for pipeline cutterhead dredges that can be considered when dredging
contaminated sediments. These controls serve the primary purpose of reducing
sediment resuspension during dredging. Many of these controls are well
founded in field observations of dredging but have not been subjected to
verification or quantitative testing.
Because the cutterhead dredge was developed to loosen densely packed deposits
and cut through soft rock, it can excavate a wide range of materials. The
cutterhead, however, may not be needed to remove soft, free-flowing sedi-
ments. Rotation of the cutterhead produces a turbidity cloud that may escape
from the dredge. Common practice is to use the cutterhead whether it is
2-11
-------
TABLE 2-2
SPECIFICATIONS FOR TYPICAL CUTTERHEAD DREDGES
WORKING IN COMMENCEMENT BAY
Dredge
Type
Pipeline
Diameter
Pipeline
Dre
H.P.
dge Pumps
Size Drive
Production
Rate
C.Y./HR
Maximum
Dredging
De pth
FT
Maximum
Depth of
Single Pass
Excava t ion
IN
Cutterhead
6
175
8
Diesel
71
12
18
Cutterhead
8
175
8
Diesel
79
12
18
Cutterhead
10
335
12
Diesel
225
25
18
Cutterhead
12
520
14
Diese 1
405
25
18
Cutterhead
14
520
16
Diese1
525
25
21
Cut terhead
16
1,125
18
Diese 1
656
40
21
Cutterhead
20
1,700
24
Diesel
1,024
50
24
Cutterhead
24
2,250
24
Diese1
1,211
50
30
Cu t terhead
30
3,600
30
Diese 1
1,875
50
36
needed or not, for debris control and because of the effort needed to remove
it. With the cutterhead removed, the cutterhead dredge becomes, in effect, a
plain suction dredge with reduced turbidity during dredging. It could remove
the softer shoaled materials such as those found in inner Sitcum Waterway and
leave the hard packed, native materials below. This would be especially
useful when the softer surface materials contain the majority of the contami-
nants. If the cutterhead is required for effective operation, turbidity
caused by conventional cutterhead dredging can be reduced by controlling the
cutter r.p.m.'s and swing speed. Since optimum r.p.m.'s and swing speed will
vary with each dredge and type of material, experimentation will be required.
Large sets and very thick cuts should be avoided since they tend to bury the
cutterhead and may cause increased resuspension if the suction cannot pick up
all of the dislodged material.
The leverman should step the dredge forward so that the cutterhead will cover
as much of the bottom as possible. This minimizes the formation of windrows
or ridges of partially disturbed material between the cuts; these windrows
tend to slough into the cuts and the material in the windrows may be suscepti-
ble to resuspension by ambient currents and turbulence caused by the cutter-
head. Windrow formation can be eliminated by swinging the dredge in close
concentric arcs over the dredging area. This may involve either modifying the
basic stepping methods used to advance the dredge or using a walking spud
system (see dredge modifications below).
2-12
-------
Side slopes of channels are usually dredged by making a vertical box cut; the
material on the upper half of the cut then sloughs to the specified slope,
resuspending sediment as it falls. The specified slope should be cut by
making a series of smaller boxes. This method, called "stepping" the slope,
will not eliminate all sloughing but will help to reduce it.
On some dredging projects, it is more economical to roughly cut and remove
most of the material, leaving a relatively thin and irregular layer for final
cleanup after the project has been roughed out. However, this remaining
material may be subject to resuspension by ambient currents or prop wash from
passing ship traffic. Requiring complete removal on each pass will reduce
this resuspension.
Loss of volatile contaminants during hydraulic pipeline transport and dis-
charge of slurried dredged material could be partially prevented by reducing
air space in the pipeline and by submerging the pipe end in the disposal site
pond. Reducing the air space would result in a loss of pumping efficiency due
to over pumping the slurry. The submerged pipeline would require constant
moving to ensure sediment dispersion within the site. This technique is
likely only applicable to fine-grained materials. Neither of these techniques
has been field tested.
f. Dredge Modifications. Recent modifications to pipeline dredges have
improved their production capabilities and reduced dredging sediment resuspen-
sion. Greater production rates are achieved by pumping a higher solids con-
centration which reduces the quantity of return water which may be contaminated
and require treatment.. Recant modi fications considered here include walking
spuds, ladder pumps, flow and density instrumentation, and underwater video
and sensor equipment.
A recent improvement in cutterhead pipeline dredges is the addition of the
walking spud. This is a hydraulic ram connected on a horizontal platform to
the spud gantry which can advance the dredge up to 40 feet without taking a
step (figure 2-4). Using the walking spud, the dredge does not have to stop
pumping sediments to move forward. Lost pumping time or increased pumping of
water during dredge stepping is eliminated. Walking spuds are common on
European dredges; however, few dredges have them in the United States; none
are located in the Pacific Northwest.
Photograph 2-1 shows an additional pump located on the ladder of the dredge.
Called a ladder pump, this pump is underwater during normal dredging opera-
tions and supplies the dredge slurry to the main pump under slight pressure.
This allows the main pump to use all of its available power to transport
dredged materials. It increases the percentage of solids pumped and dredge
production.
The addition of flow gages and nuclear density gages provide the dredge
operator with instant production data. This information can be used to make
adjustments to optimize production, such as adjusting cut depth, cutter
rotation, ladder swing, etc.
2-13
-------
40'
APPROX.
HYDRAULIC RAM
DREDGE
SPUD
Figure 2-4: Walking Spud
2-14
-------
Closed circuit underwater video camera's and water sensors can be mounted on
the dredge ladder and used to monitor turbidity in vicinity of the cutter-
head. Adjustments can be made in cutter rotation speed (r.p.m.'s) and swing
speed to minimize resuspension of dredged materials. Video cameras are only
effective when dredging in relatively clear waters. Sensors are best used in
turbid waters.
Loss of volatile contaminants associated with gas present in the sediments in
situ could be substantially reduced by collecting and treating gas from dredge
degasser systems. To date, the only known application of this was done by the
Dutch. Gases were fed into the dredge furnace and discharged with engine
emissions; water and sediment obtained from the degasser was injected into the
discharge pipeline. Gas quantities collected and contaminant incineration
efficiencies were not monitored. Collection of materials from the degasser
system also avoids the sediment resuspension resulting from degasser systems
that commonly discharge into the water column.
Loss of volatile contaminants during discharge could be partially reduced by
placing a shroud over the discharge opening in order to collect the volatiles.
This idea has not been developed or field tested.
2.02.02. Suction and Dustpan Dredges.
a. Description of Equipment. Both suction and dustpan dredges are
conventional pipeline dredges with modified dredging heads. They have many
similarities and are only briefly discussed below.
The suction dredge is a pipeline cutterhead dredge with the cutterhead removed
(figure 2-5). Many times skid plates under the ladder and a vertical elbow on
the suction are added to improve operations.
The dustpan dredge is a hydraulic suction dredge that uses a widely flared
dredging head along which are mounted pressure water jets (figure 2-6). The
jets loosen and agitate the sediments which are then captured in the dustpan
head as the dredge itself is winched forward into the excavation. This type
of dredge was developed by the Corps of Engineers to maintain navigation
channels in uncontrolled rivers with bedloads consisting primarily of sand and
gravel (e.g., Mississippi River).
b. Description of Operation. The operation of the suction dredge is the
same as that of the cutterhead pipeline dredge (paragraph 2.02.01(b) above).
The dustpan dredge moves by winching itself forward to anchors set upstream of
the dredging area. The dustpan dredge maintains navigation channels by making
a series of parallel cuts through the shoal areas until the required widths
and depths are achieved.
c. Characteristics. The production rates and dredging depths for the
suction and dustpan dredge are comparable to those for cutterhead pipeline
dredges shown in tables 2-1 and 2-2. One difference to note is that the
dustpan dredge can excavate very thick cuts (up to 6 feet) on a single pass.
2-15
-------
ANCHOR LINE
ANCHOR LINE
DISCHARGE PIPE
SUCTION PIPE
Figure 2-5: Plain Suction Dredge
2-16
-------
A FRAME
DISCHARGE PIPE
ANCHOR
LINES
DUSTPAN
LADDER
//MW
Figure 2-6: Dustpan Dredge
2-17
-------
Dustpan dredges are: (1) all in the large dredge class with 30-inch pipelines
or larger, (2) all located on the Mississippi River or its tributaries, and
(3) all (with one exception) operated by the Corps of Engineers.
d. Equipment and Operational Considerations. Suction dredges generate
low levels of turbidity. However, they are limited to dredging soft, free
flowing, and unconsolidated materials. Trash logs and debris in the dredge
materials will clog the suction and greatly reduce the effectiveness of the
dredge.
The dustpan dredge was designed for a specific purpose and, for this reason,
there are certain limitations to its use in other dredging environments such
as Commencement Bay. It can dredge only loose materials such as sands and
gravels. Most dustpan dredges have relatively low discharge pressure pumps
and are not particularly well suited or designed for transporting dredged
material long distances to upland disposal sites. Pumping distances are
limited to about 1,000 feet without the use of booster pumps.
e. Operational Control and Dredge Modifications. With the exception of
cutterhead controls, applicable operational controls for a suction dredge are
similar to those for a cutterhead dredge (see paragraph 2.02.01.e.). For
dustpan dredges, the angle of the water jets on the head and the water pressure
from these jets can and should be adjusted to achieve the minimum amount of
sediment resuspension.
2.02.03 Hopper Dredges.
a. Description of Equipment. Hopper dredges are self-propelled, seagoing
ships from 180 to 550 feet in length with either barge-type hulls or molded
hulls with the lines of ocean vessels (figure 2-7). They are equipped with
propulsion machinery, sediment containers called hoppers, dredge pumps, and
other special equipment. Dredged materials are raised by large centrifugal
pumps through drag pipes connected to dragheads that are in contact with the
channel bottom (figure 2-8 and photograph 2-4). Dredged materials are then
discharged into the hoppers. Hopper dredges are classified according to
hopper capacity: large class hopper dredges have hopper capacities of 6,000
cubic yards (c.y.) or greater, medium class hopper dredges have hopper capa-
cities of 2,000 to 6,000 c.y., and small class hopper dredges have hopper
capacities of 500 to less than 2,000 c.y. Presently located in the Pacific
Northwest are medium and small class hopper dredges. They are equipped with
twin propellers, twin rudders, and bow thrusters to provide required maneuver-
ability. Track plotting surveying equipment can be placed aboard for exact
positioning of the dredge.
b. Description of Operation. The operation of a hopper dredge in
Commencement Bay would involve greater effort than that required for the
ordinary handling of an ocean cargo vessel, which is usually attached to a tug
and navigating the centerline. The dredge will usually operate near the edge
of the channel using its own power to stay in the dredging area. Dredging is
accomplished by repetitive passes over the area to be dredged, each pass
removing inches of surface material. During dredging operations, hopper
2-18
-------
Dragarms (A) with dragheads (B) extend from each side of the ship's hull The dragheads
are lowered to the channel bottom and slowly pulled over the area to be dredged Pumps
(C) create suction in the dragarm and the silt or sand is drawn up through the arms and
deposited in hopper bins (D) in the vessel's midsection When the bins are full, the dredge
sails to the designated disposal area and empties the dredged material through large
hopper doors (E) in the bottom of the hull
FIGURE 2-7: TYPICAL HOPPER DREDGE COMPONENTS
2-19
-------
' ^ 11
v \ L
Photograph 2-4: Hopper Dredge California Draghead
CLEAN-OUT
jOI , iOI . iiOJ -
.£11
Al
I OS
f
J
W" imr
1
W-
TOP VIEW
r
SECTION A-A
WATER INLET CONN
VALVE GATE
HEEL PAD
GRATE
SIDE VIEW
Figure 2-8: Hopper Dredge California Draghead
2-20
-------
dredges travel at a ground speed of 2 to 3 miles per hour and can dredge in
depths of about 10 to 60 feet. The draghead is moved along the channel bottom
as the vessel moves forward. The dredged material is sucked up through the
drag pipe and deposited in the hoppers of the vessel where it settles. As the
hopper is filled, overflow water is usually discharged at the site of dredg-
ing. Once loaded, hopper dredges cease dredging and move to the disposal site
to unload. The hopper is considered to be full once an economic load has been
achieved. The economic load is based on the pumping time required to obtain
the least cost per c.y. of solids dredged and discharged. It considers
pumping and nonpumping times (travel to disposal site and back) of the entire
dredging cycle and considers only solids (suspended and settleable) that make
it to the disposal site (not overflow loss). Usually the economic load, which
will vary by equipment, disposal site location, and sediment characteristics,
is specified as a maximum overflow pumping time that allows the greatest
possible amount of dredged material to settle in the hopper. For some
exclusively fine-grained materials which may remain in a slurry, the economic
load may not require overflow pumping.
c. Characteristics. Hopper dredge characteristics are extremely variable.
Hopper sizes vary from 500 to 8,000 c.y., and pumping rates per minute from 15
to 150 c.y. Minimum dredging depth is limited by the draft of the dredge,
from 12 to 28 feet, and maximum dredging depth varies from 45 feet to 80 feet.
d. Equipment and Operational Considerations. Hopper dredges can be used
to transport dredged materials greater distances than pipeline dredges.
Hopper dredges, though not precise in dredging location (horizontal accuracy
often cannot be controlled to less than a 10-foot tolerance), can remove a few
inches of contaminated materials from the bottom with each pass. They can
dredge shoals that slope or vary in elevation. Few other types of dredges are
capable of doing this. However, the hopper dredge cannot dredge effectively
along piers or near structures. Hopper dredges are often the most economical
type of dredge to use where disposal areas are not available within economical
pumping distances of hydraulic pipeline dredges. The hopper dredge provides
self-contained storage of dredged material which eliminates the need for
separate barge, scow, or pipeline.
As discussed for pipeline dredges above, modification of hopper dredges to
collect gases from the degasser system and shrouding of the hopper bin to
capture gases discharged from the pipe are potential dredge modifications that
could be used to reduce loss of volatile contaminants during dredging. These
modifications have not been attempted to date.
The hopper dredge can be mobilized and initiate dredging in a relatively short
period of time. Hopper dredges have excellent maneuverability and can work
effectively in congested harbors such as Commencement Bay.
e. Operational Control. The hopper dredging of contaminated materials
may be restricted by pumping or loading the hopper bins with dredge slurry and
not allowing overflow. This would result in a load that would be approxi-
mately 80 percent water and 20 percent sediments for silty sands found in
2-21
-------
Commencement Bay. This compares to an average of 70 percent sediment using an
economic load. The rate of solids loss in the overflow (which may determine
if overflow is acceptable) will vary with amount of water in the hopper,
hopper capacity and drainage characteristics, material characteristics
(settleability) , pumping rate, and elapsed time of overflow.
2.02.04 Special-Purpose Dredges. Special-purpose dredging systems have been
developed during the last few years in Japan, Europe, and the United States to
pump dredged material slurry with a high solids content and/or to minimize the
resuspension of sediments. Most of these systems are not intended for use on
typical maintenance operations; however, they do provide alternative methods
for dredging projects involving contaminated sediments that require more
careful handling. The special-purpose dredges that appear to have the most
potential in limiting resuspension are shown table 2-3, taken from Herbich and
Brahme (in press). A description of each dredge follows.
a. Mudcat Dredge. The mudcat is a small, hydraulic dredge designed to
remove mulch, weeds, sand, municipal sludge, and industrial wastes. Dredging
depth is limited to 15 feet or less. It is portable and designed for projects
where a production of 50 to 130 c.y./hour at up to 30 percent solids is suffi-
cient. Instead of a conventional cutter, the mudcat has a horizontal cutter-
head equipped with cutter knives and a spiral auger that cuts the sediment and
moves it laterally towards the center of the auger where it is picked up by
the suction (figure 2-9). It can remove sediments in an 8-foot width with a
depth of cut of up to 15 feet. The mudcat leaves the bottom flat and free of
the windrows that can be pushed up between swings in cutterhead dredging
operation. A retractable shield shrouds the cutterhead, entraps suspended
material, and minimizes turbidity (Herbich and Brahme, in press).
During monitoring, Herbich and Brahme (in press) report that near bottom
suspended solids concentrations 5 feet from the auger were slightly greater
than 1,000 mg/1 relative to the background concentration of 500 mg/1. Surface
and middepth concentrations measured 5 feet and 10 feet in front of the auger
were typically less than 200 mg/1 compared to the background values of 40 to
65 mg/1. In general, the turbidity plume was confined to within 20 feet of
the dredge. Studies at Vandalia Reservoir showed suspended solids concentra-
tions of between 100 and 300 mg/1 at the auger (Barnard, 1978).
Mudcat dredges are available on the Pacific Coast. They are compact and
readily transportable by truck or air and can be operated in confined and
isolated areas with shallow waters. However, the limited dredging depth (less
than 15 feet) constrains its use to intertidal areas or low tide periods in
Commencement Bay.
b. Pneuma Pump. The pneuma system was the first dredging system to use
compressed air instead of centrifugal motion to pump slurry through a pipe-
line. It has been used extensively in Europe and Japan. According to the
literature published by the manufacturer, this system can pump slurry at a
relatively high solids content with little generation of turbidity. The
operation principle is illustrated in figure 2-10. During the dredging
process, the pump is submerged and sediment and water are forced into one of
the empty cylinders through an inlet valve. After the cylinder is filled,
2-22
-------
DISCMARGE LINE
ANCHOR
LINE
AUGER
Figure 2-9: Mudcat Dredge
2-23
-------
FILLING PHASE
DISCHARGE PHASE
WATER
SURFACE
V
COMPRESSED
A!R \
DISCHARGE
INLET
VALVE
INLET
Figure 2-10: Operating Cycle of the Pneuma Pump
2-24
-------
TABLE 2-3
SUSPENDED SEDIMENT LEVELS PRODUCED BY VARIOUS SPECIAL-PURPOSE DREDGES
Name of Dredge Suspended Sediment Level
Mudcat Dredge 5 feet from auger, 1000 mg/1 near bottom
(background level 500 mg/1)
5 to 12 feet in front of auger, 200 mg/1 surface
and middepth (background level 40 to 65 mg/1)
Pneuma Pump 48 mg/1 3 feet above bottom
4 mg/1 23 feet above bottom (16 feet in front of
pump)
Cleanup System 1.1 to 7.0 mg/1 above suction
1.7 to 3.5 mg/1 at surface
Oozer Pump 6 mg/1 (background level) 10 feet from head
Refresher System 4 to 23 mg/1 at 10 feet from head
compressed air is supplied to the cylinder, forcing the water out through an
outlet valve. When the cylinder is almost empty, air is released to the
atmosphere, producing atmospheric pressure in the cylinder. The pressure
difference between the inside and outside of the cylinder creates a suction
that forces sediment into the cylinder. When the cylinder is filled with
sediment, compressed air is again pumped into the cylinder to expel the sedi-
ment from the cylinder. The capacity of a large plant (type 1500/200) is
2,600 c.y./hour. The system has been used in water depths of 150 feet; how-
ever, 500 feet depths are theoretically possible.
Field tests on a pneuma model 600/100 were conducted by the WES of the U.S.
Army Corps of Engineers (Richardson, et al., 1982). The results of turbidity
monitoring, although not definitive, seemed to support the manufacturer's
claim that the pneuma pump generates a low level of turbidity when operated in
loosely consolidated, fine-grained sediments. It was also found that the
pneuma pump was able to dredge at almost in situ density in a loosely com-
pacted silty clay typical of many estuarine sediments. The pneuma system was
used successfully in PCB cleanup operations on the Duwamish Waterway in
Seattle, Washington, in 1976. The pneuma pump, however, was not able to
dredge sand at in situ density. The only pneuma-type dredge available in the
United States at this time is operated by Namtex Corporation of Chicago,
Illinois. The pneuma system is crane supported and thus can be operated in
confined areas using various structural mounts. It dismantles easily for
truck or air transport and can be operated in most water depths. Cables and
pipelines used for the system will create temporary obstructions to navigation.
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c. Oozer Dredge. The oozer dredge system was developed by Toyo Con-
struction Company, Japan. The dredge operates in a manner similar to the
pneuma pump system; however, there are two cylinders (instead of three) and a
vacuum is applied during the cylinder filling stage to achieve more rapid
filling of the cylinders. The dredge system is usually mounted on a ladder
and is equipped with special suction and cutterheads depending on the type of
material being dredged. Dredging depth is limited only by the depth the
ladder can reach. Dredging conditions, such as the thickness of sediment
being dredged, bottom elevation after dredging, and amount of resuspension,
are monitored by high frequency, acoustic sensors and an underwater television
camera. A large oozer dredge has a dredging capacity ranging from 400 to 650
c.y./hour, producing a slurry of up to 80 percent of in situ sediment density.
During one dredging operation, suspended solids levels within 10 feet of the
dredging head were all within background concentrations of less than 6 mg/1
(Herbich and Brahme, in press).
d. Cleanup System. To avoid resuspension of sediment, Toa Harbor Works
of Japan developed the unique cleanup system for dredging highly contaminated
sediment (Sato, 1976). The cleanup head consists of a shielded auger on the
front end of a pipeline dredge. The head collects sediment as the dredge
swings back and forth and the shield guides the sediment towards the suction
of a submerged centrifugal pump (figure 2-11). To minimize sediment resuspen-
sion, the auger is shielded and a movable wing covers the sediment as it is
being collected by the auger. The resulting slurry consists of 30 to 40 per-
cent solids by weight. Sonar devices indicate the elevation of the bottom.
An underwater television camera is used to show material being resuspended
during a dredging operation. Suspended sediment concentrations around the
cleanup system ranged from 1.7 to 3.3 mg/1 at the sediment surface to 1.1 to
7.0 mg/1 at 10 feet above the suction equipment, relative to the background
near surface levels of less than 4.0 mg/1 (Herbich and Brahme, in press).
e. Refresher System. Another dredging method designed recently by the
Japanese is the refresher system. The refresher uses a helical-shaped gather
head to feed the sediments into the suction with a cover over the head to
reduce resuspension (see figure 2-12). The refresher also uses an articulated
dredge ladder to keep the head level to the bottom over a wide range of
dredging depths. During several comparison tests in similar material, the
refresher system produced suspended sediment levels of from 4 to 23 mg/1
within 10 feet of the dredge head as compared to 200 mg/1 with a conventional
cutterhead dredge. Production for the cutterhead (26-inch discharge) was 800
c.y./hour, while production with the refresher system (17-inch discharge) was
350 c.y./hour. The researchers felt that the refresher system produced
one-fifteenth of the total resuspension produced by the operation of a cutter-
head dredge (Kaneko et al, in press).
f. Availability of Cleanup, Oozer, and Refresher Dredges. The cleanup,
oozer, and refresher dredges are all Japanese-manufactured equipment. The
oozer pump is not presently well known or available to United States markets,
and its use would likely require a specific international, Goverment, or
private agreement. The cleanup and refresher dredges, modifications to the
ladder and head of pipeline dredges, may be available and marketed in the
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DIRECTION OF SWING
TO PUMP
GAS
COLLECTING
SHROUD
V
SHUTTING PLATE
AUGER
WING
WING
I BOTTOM SEDIMENT
Figure 2-11: Clean-Up System Dredgehead
2-27
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UNDERWATER
TV CAMERA
><+—-SHUTTER
SUCTION
CONTROL PLATE~
HYDRAULIC
CYLINDER -
GATHER HEAD
GAS COLLECTOR
SWING DIRECTION
RUBBER PLATE
A. FRONT VIEW
UNDERWATER TV CAMERA
TURBIDISENSOR ^ [fTD
MONITOR PLATE
COVER
-4
GATHER HEAD
B. SIDE VIEW
Figure 2-12: Refresher System
2-28
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United States in the near future. However, as with most special-purpose
dredges, additional research, development, and experience are needed to fully
determine their application and limitations.
2.03 Mechanical Dredges. Mechanical dredges are characterized by the use of
some form of bucket to excavate and elevate the bottom materials. They do not
transport the material to the ultimate deposition area except in the infrequent
instances where the material can be deposited on the bank or behind a dike or
seawall immediately adjacent to a narrow waterway. Normally the mechanical
dredge releases materials into a barge, which then transports the material to
the disposal site.
Mechanical dredges can be categorized into three subgroups as a function of
how their buckets are connected to the dredge: wire rope connected, struc-
turally connected, and chain and structurally connected.
Examples of wire rope mechanical dredges are the clamshell, dragline, and
orange-peel dredges. These dredges are frequently called simply "bucket"
dredges. Examples of structurally connected mechanical dredges are the power
shovel and the backhoe dredges. The only example of the third subgroup is the
bucket ladder or bucket line dredge which dredges continuously using multiple
buckets mounted on an endless chain. This report will address only bucket
dredges; other mechanical dredges were discussed in section 2.0L.03 above.
a. Description of Equipment. The bucket dredge is so named because it
utilizes a bucket to excavate the materials to be dredged (figure 2-13).
There are different types of buckets to accomplish various types of dredging
and buckets can be changed to suit operational requirements. For this report,
the term "bucket dredge" will refer primarily to the clamshell bucket.
Buckets range in capacity from 1 to 18 c.y. and are attached to a crane by
wire rope. The crane is pedestal mounted on a flat-bottom barge. In most
cases, anchors and spuds are used to position and move the barge. By using
the anchors alone, the vessel can work in water that is deeper than spud
length. The effective working depth is limited to approximately 100 feet.
Bucket dredges load dredged material into scows or barges that, are towed to
the disposal site.
b. Description of Operation. Most bucket dredges are not self propelled,
but can move over a limited area during dredging by manipulating the spuds,
anchors, and crane boom. After placing anchors and spuds the dredge drops the
open bucket into the sediments. The jaws of the bucket are closed shearing
material from the bottom, and the bucket is raised above the water surface and
swung over the barge where the sediment is released. As the bottom of the
waterway is dredged to the desired depth, the dredge is moved forward.
c. Characteristics. The bucket dredge typically operates at speeds of 30
to 60 buckets per hour. Larger buckets generally resuspend less material per
c.y. removed and are more cost effective. Because of this, only medium and
large bucket sizes were considered for possible use in Commencement Bay.
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~E
SPUDS
Figure 2-13: Bucket Dredge
2-30
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d. Equipment and Operational Considerations. The advantage of bucket
dredges over hydraulic dredges is that they move sediments with minimum
addition of water. They should be considered for use where sediment contami-
nation is highly water soluble. Bucket dredges dredge slopes and varied
contour elevations to approximately 2-foot vertical tolerance, less accurate
than most hydraulic dredge types. However, vertical accuracy could be
increased by lowering the bucket to a specified depth and then closing rather
than dropping the full weight of the bucket. This practice is not often used
because it substantially reduces production rate, increases transport of water
(in the bucket), and reduces area of each grab (as jaws may impact bottom in a
partially closed position). This technique may be appropriate for highly
contaminated and/or unconsolidated materials located immediately on the
surface. Other considerations are listed below.
o Large bucket dredges can dredge materials from above water level to
depths of over 100 feet.
o Large bucket dredges of all sizes are readily available in Puget
Sound and the Pacific Northwest.
o Scows or barges are required to move the dredged material to the
disposal site. Mechanical or hydraulic rehandling of the dredged material is
required if the material is to be placed on an upland site.
o Bucket dredges can maneuver and operate in confined areas and are
capable of working in debris and around obstruction.
o Bucket dredges excavate materials at in situ density, resulting in
lower volumes of material to handle (no hydraulic swell factor).
e. Operational Control and Modification. Operators of bucket dredges
should overlap grabs in lieu of the conventional practice of sweeping the
bottom to level out remaining humps. This may increase cost by up to
30 percent.
In soft, unconsolidated and contaminated surface sediments, the conventional
practice of providing navigable water depth by dropping and penetrating
through the soft surface layer, removing firmer subsurface materials, and
allowing surface materials to slough into a hole will result in a low contami-
nant removal efficiency and high resuspension of contaminated sediments.
Bucket weight should be adjusted to the density of surface sediments instead.
f. Dredge Modifications. On a c.y. basis, resuspension of dredged
materials can be reduced by use of large buckets. Heavy weight, pick-tooth
buckets are used to dredge hardpacked sediments; lighter weight buckets
without teeth, called rehandling buckets, are utilized to dredge softer
sediments. By selection of weight of buckets, the depth of cut can be
controlled.
To minimize the turbidity generated by a clamshell operation, watertight
buckets have been developed. The edges seal (tongue-in-groove arrangement)
2-31
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when the bucket is closed and the top is covered to minimize the loss of
dredged material. Available sizes range from 1.3 to 18 c.y. These buckets
are best adapted for dredging fine grained material. Corps of Engineers test
comparisons of 1.3 c.y. typical clamshell and watertight clamshell indicate
that the watertight buckets generate 30 to 70 percent less turbidity in the
water column than typical buckets because leakage of the dredged material is
reduced by approximately 35 percent. Existing clamshell buckets can be
converted to watertight buckets by minor structural modifications.
2.04 Contaminant Efficiency of Dredging Methods. Chemical constituents
associated with sediments are unequally distributed among different chemical
forms and sediment phases depending on the physical-chemical conditions in the
sediments and the overlying water. When contaminants introduced into the
water column become fixed into the underlying sediments, they rarely if ever
become part of the geological mineral structure of the sediment. Instead,
these contaminants remain dissolved in the sediment interstitial water (pore
water), become sorbed to the sediment ion exchange portion as ionized con-
stituents, form organic complexes, and/or become involved in complex sediment
oxidation-reduction reactions and precipitations. Dredging of contaminated
sediments causes short-term loss of contaminants from gas, interstitial water,
or solid phases. Dredging method also influences long-term contaminant losses
at the disposal site.
2.04.01 Volatile Phase Contaminants.
a. General. There are several pathways whereby volatile contaminants
find their way through water into the sediments. The most likely pathways are:
(1) groundwater seeps;
(2) bound to particulates in industrial and municipal effluents,
these sinking to the bottom; and
(3) spills of concentrated contaminant that are heavier than water.
These processes can produce significant concentrations of volatile contami-
nants in aquatic sediments. In recent years, methods for sampling, storing,
and analyzing sediments did not allow identificaton or proper quantification
of many of these volatile compounds in the sediments.
Key factors influencing volatile contaminants loss during dredging are:
o the volume of gas present in the sediments in situ;
o the partitioning of contaminants between particulate, water, and gas
phases of the sediment;
o the degree of disturbance and agitation of the sediments produced by
dredging;
2-32
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o the surface area of the sediments exposed to air during dredging; and
o the exposure time of sediments to air during dredging.
Contaminants will vary in how they distribute themselves between sediment
phases; however, in general, contaminants with higher mobility rankings will
be found in higher concentrations in the gas phase of the sediment than those
with lower ranking (see appendix 1). The amount of gas in the sediments is
not well documented and represents a key information need in making quantita-
tive predictions of volatiles loss during dredging.
Hydraulic and mechanical dredging differ in several ways in the degree of
sediment disturbance, the exposure time to air, and the surface area exposed.
These are discussed below and provide the basis for evaluating performance of
these dredging techniques.
b. Hydraulic Dredging. Hydraulic dredging moves sediments in a water
slurry. This process represents a greater disturbance of the sediments than
mechanical dredging and, therefore, results in greater loss of in situ gas and
associated volatile contaminants. As a result, most hydraulic dredges (pipe-
line and hopper) have degassing systems to remove gas from the intake pipe
prior to the main pump. The gas, which causes cavitation and wear of pump
impellers, is discharged, along with a small amount of water and sediment into
the water column or atmosphere. This degassing system provides the greatest
potential loss of volatiles during the dredging process.
During transport of the slurry in the discharge pipe, some air is entrained
from the small air space in the pipe. This air space and entrained air, which
increase towards the discharge end of the pipe, allow additional loss of
volatile contaminants. Upon discharge in an upland or nearshore site, air
from the air space is lost to the atmosphere. In hopper dredges, the loss of
volatiles occurs as the sediment slurry is discharged into the bin.
For pipeline dredging, the slurry may lose additional volatiles upon impact
with the settling pond. The sudden reduction in pressure from iji situ
conditions before and after impact may increase the loss. After impact,
volatile contaminants may be lost as the slurry runs out over a delta of
dredged sediment. This shallow water and turbulent flow distribution of the
slurry favors desorption and loss of contaminants as the surface area to
volume ratio would be maximized
at this point.
However, the dredging and transport process for hydraulically dredged sedi-
ments provide relatively brief exposure time to air. Over time, the processes
governing equilibruim partitioning of contaminants in the sediments JLn situ
will potentially concentrate volatiles in the available gas phase. Once in
situ gas has been lost during dredging, there would be little opportunity for
additional, substantial loss of volatiles in the disposed material. Overall,
the loss of the most volatile contaminants found in the sediments is likely
not to exceed 10 to 20 percent (assuming a large in situ gas volume).
2-33
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Techniques for reducing loss of volatiles during hydraulic dredging are
mentioned above: collection and treatment of gas from degassing systems;
elimination of air space in discharge pipe by less efficient, full-pipe pump-
ing; shrouding the discharge end of the pipe or the hopper bin to collect
volatile contaminants; and submerging the discharge end of the pipe. Of
these, priority for research and field experience should focus on collection
of gas from degassing systems.
c. Mechanical Dredging. Mechanical dredging causes substantially less
disturbance to the sediments than does hydraulic dredging. Additionally, the
surface area to volume ratio of the sediments that are stockpiled on a trans-
port barge is relatively low. The time that sediments remain exposed to the
air is usually longer than for most hydraulic dredging jobs; however, the low
disturbance and low surface area exposure substantially override the effect of
longer exposure time. As a result, loss of volatile contaminants is less for
mechanical dredging than for hydraulic dredging.
2.04.02 Soluble Phase Contaminants.
a. General. As with volatile contaminants, contaminants with a higher
mobility ranking can be expected to have a higher concentration in the sedi-
ment interstitial water than those with a lower ranking. Quantitative
predictions of the amount of any particular contaminant to be found in
solution could be estimated by use of the contaminant specific partitioning
coefficients and the volumes of sediment and interstitial water present.
Again, key factors in the loss of soluble contaminants during dredging are the
degree of sediment disturbance and the exposure of the sediments to additional
wacer. In addition, the efficiency of a dredge at removing the liquid phase
of a sediment is critical to the amount of soluble contamination lost.
b. Hydraulic Dredging. In hydraulic dredging, the use of water to move
sediments will extract and dilute the interstitial waters and will expose the
sediments to additional water that can provide for release of soluble contami-
nants from particle surfaces. The amount of contaminant that goes into solu-
tion will depend on a number of factors, including the contaminant's mobility,
the types and relative strengths of binding surfaces, and the chemical condi-
tions in the dredging site and slurry water.
Because the hydraulic dredge is designed to pump water, its removal of the
liquid phase of the sediments is highly efficient, resulting in relatively
little loss of soluble contaminants at the dredging site when compared to
mechanical dredging. However, this slurry becomes a large volume of effluent
that may require treatment at the disposal end of the process (or may be lost
in hopper dredge overflow). After removal of the effluent, hydraulically
dredged sediments typically produce greater quantities of water during
dewatering than sediments mechanically dredged.
c. Mechanical Dredging. Mechanical dredges lose some of the interstitial
water during the lift through the water column and in dewatering during trans-
port. However, in comparison to hydraulic dredging, reduced disturbance and
2-34
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the absence of a slurry results in less opportunity for sediment-bound con-
taminants to go into solution. Dewatering of the material at the disposal
site also produces less water than hydraulically dredged sediments. However,
the efficiency of mechanical dredges at removal of the liquid phase of sedi-
ments is low in comparison to hydraulic dredging. During dredging and trans-
port dewatering the loss of this phase could result in substantial loss of the
more soluble contaminants, especially in less cohesive and coarser sediments
that dewater rapidly. The use of watertight buckets and sealed transport
containers (e.g., watertight barges) would significantly reduce this loss.
2.04.03 Sediment-Bound Contaminants. The vast majority of heavy metals and
organic contaminants are associated with the fine-grained and organic com-
ponents of the sediment. With certain exceptions such as ammonia, they tend
to remain bound to particles during the dredging and disposal process. There-
fore, the control of solids during dredging is highly correlated to the con-
trol of overall contamination. Greater turbidity and sediment resuspension
levels for a given dredge result in lower removal efficiency, less confinement,
and greater release of contaminants.
As a general rule, hydraulic dredges remove a greater percentage of the sedi-
ments at a dredging site than mechanical dredges. This is reflected in the
lower sediment resuspension values for hydraulic dredges. However, to some
extent, this is a function of the type of head being used. Active dredge
heads (e.g., cutterhead) will often produce bottom turbidity equivalent to
mechanical dredges. Passive heads (e.g.; plain suction, Pneuma) produce
substantially less resuspension of sediments. The advent of shrouded, active
dredge heads (mudcat, refresher, cleanup dredges) provides for removal effi-
ciency, debris control, and lower resuspension throughout the water column.
The hydraulic dredge breaks up the cohesion of in situ sediments. This makes
the dredged sediment more difficult to consolidate and control at the disposal
site than for mechanically dredged sediments. For hopper dredging, these
suspended sediments and any associated contaminants will be lost at the
extraction site if overflow is allowed.
Overall, the biggest differences between hydraulic and mechanical dredging
sediment resuspension is seen in the middle and top portions of the water
column (with the exception of hopper dredge overflow).
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CHAPTER 3.0 DISPOSAL METHODS AND SITES
3.01 Introduction. Proper selection of dredging equipment and dredging
technique is essential to economically remove and control contaminated sedi-
ments at the dredge site. However, disposal of these sediments is of equal or
greater importance to project viability from environmental and economic stand-
points. Implicit within the selection of a preferred disposal method or site
are the efficiency of the dredging operation, the efficiency of the disposal
method or site to retain the contaminants of concern, and the level of treat-
ment and monitoring to be assumed to assure continued confinement or a con-
trolled, acceptable release of those contaminants. Following a discussion of
dredged material behavior when discharged from various dredges, this chapter
discusses three generic disposal methods, open water, upland, and nearshore,
in addition to off-site considerations as they apply to these three major
methods. Secondly, a contaminant evaluation, similar to the one included in
the previous chapter, examines the strengths and weaknesses of the generic
disposal methods in successfully containing the various contaminant classes.
Thirdly, specific disposal sites in the Commencement Bay area are identified
based on criteria developed for this report. These sites are discussed and
evaluated for their ability to meet anticipated needs for disposal of contami-
nated sediments from Commencement Bay. Although no sites outside of the
Commencement Bay area are listed, options and limitations for off-site
disposal are briefly addressed.
In our evaluation of disposal methods and sites, three major factors were
cons idere d:
o Cost - Includes site preparation, transportation, and other
costs associated with initial or ongoing disposal of
sediment, discussed in chapter 5.
o Limitations - Includes factors such as ownership, availability,
capacity, location of material source, environmental
effects on significant resources, and identification of
data and information gaps.
o Containment - Includes the effectiveness in meeting the goal of maximum
containment and minimum release of contaminants.
3.02 Transportation and Discharges from Various Types of Dredges. In order
to assess the opportunities and problems associated with the disposal methods,
some understanding of the behavior and characteristics of dredged material
discharges from the various types of dredges is necessary. This will include
transportation considerations as they bear on disposal operations. Chapter 2
dealt with sediment behavior as those sediments were removed from the dredge
site. In this chapter, sediment behavior during the disposal operation is
descr ibed.
3-1
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a. Hopper Dredge. Hopper dredge characteristics are discussed in the
previous chapter. During normal operations, once the hoppers have been
filled, the drag arms are raised and the hopper dredge proceeds to the dis-
posal site. During transport to the disposal site, the sediments tend to
settle out and consolidate within the hopper. At the disposal site, the
dredged materials are bottom dumped or pumped out and the dredge returns to
the dredging site to reload.
Bottom dumping from hopper dredges normally involves open-water disposal.
Most older hopper dredges dispose of the dredged material through hinged
hopper doors in the bottom of the ship's hull which allows the materials to be
spread over a site or dumped at once. Many of the newer hopper dredges are of
the "split hull" design chat dumps the entire load at once. Bottom-dump
disposal produces a series of discrete discharges at intervals between one and
several hours. When discharged, the dredged material falls through the water
column as a well defined jet of high density fluid (figure 3-1). Ambiont
water is entrained during descent. Depending on tlx; composition of the
dredged material, most of it comes to rest on the bottom as a high density,
fluid mass. Some material is carried away from the impact point by the
horizontally spreading bottom surge created by the impact. This spread may
extend a few hundred feet from the point of impact, settling as the turbulence
of the surge dissipates. If a strong pynocline is present in the water
column, some suspended finer material may concentrate and spread at this
point. Testing with sediments from or equivalent to the site to be dredged
would be necessary to determine whether a substantial loss of fines could be
expected from hopper dredge discharge.
Some hopper dredges are equipped with pump out capability. Pump out discharge
can be used for any disposal njethod. Dredges with this capacity have the
flexibility to pump directly, bypassing the hopper, discharging like a con-
ventional cutterhead pipeline dredge. Conventionally, the hopper dredge will
fill its hopper, move to the discharge point and either pump the material
overboard, inject it into the water column at depth, or pass the slurry
through a pipeline to a nearshore or upland disposal site. Sediment behavior
from this disposal operation will be very similar to that described for the
cutterhead pipeline dredge.
b. Mechanical Dredge. Mechanical dredges remove the sediment at approxi-
mately jji situ density. The sediment is placed in barges or scows for trans-
port to an open-water disposal area or for rehandling directly into a confined,
nearshore disposal area. The sediments can also be carried by trucks or other
land conveyance. During transport there is usually very little return water
to the aquatic environment, especially if the container is watertight. Some
of the interstitial water will drain from the material. Although several
barges may be used so that the dredging is essentially continuous, disposal
normally occurs as a series of discrete discharges. In open-water disposal,
the dredged material may be fluid mud similar to that in a hopper dredge , but
often sediments that are mechanically dredged remain consolidated as large
clumps and reach the bottom in this form with little release of interstitial
water. The dredged material descends rapidly through the water column to the
3-2
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CURRENT
DISPOSAL SITE BOUNDARY
Figure 3-1. Bottom Dump Disposal of Dredged Material
From a Hopper Dredge
bottom, and only a minor fraction of the material remains suspended. Option-
ally, sediments in the barge can be reslurried and discharged through a
pipeline to any type of disposal site.
c. Cutterhead Pipeline Dredge. Hydraulic dredges, which include hopper
dredges, produce a slurry of sediment and water. Transportation of the mate-
rial through the discharge pipeline, however, differs dramatically from both
hopper and mechanical dredges as the dredging and disposal operations are self
contained and continuous. The material removed by the dredge is pumped in
slurry through a continuous pipeline to the disposal area and discharge con-
tinues as long as the dredge is operating. Generally, a pipeline dredge can
pump its slurry a limited distance from the dredge site; transporting the
slurry further within the pipeline requires a booster pump. The original
pumping distance varies according to the size of the dredge, the sediment type
3-3
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being pumped, and the topography over which it is being pumped. Upon dis-
charge, coarse material, such as gravel, clay balls, or coarse sand, imme-
diately settles in the disposal area and usually accumulates directly in front
of the discharge point. At an open-water site, the fine-grained material
settles to the bottom where it forms a low gradient circular or elliptical
fluid mud mound on top of the coarser material that has already settled. The
suspended plume is subjected to current movements that can transport it out of
the disposal area. In confined disposal areas, fine-grained material will
settle out to the extent allowed by available settling area and retention time
of the site.
3.03 Disposal Methods. For purposes of this report, all disposal methods
include subsequent capping of contaminated sediments with cleaner material.
For open-water disposal, the cap serves to isolate the contaminated material
from direct interaction with the overlying water body. For upland and near-
shore disposal, the cap retards water infiltration from precipitation, prevents
windborne erosion, and direct interaction wilh the human en v i roninen t.
3.03.01 Open-Water Disposal. Open-water disposal is the deposition of
dredged material at an aquatic site followed by capping with cleaner sedi-
ments. Possible disposal sites in Commencement Bay range in water depth from
500 feet to less than 100 feet. Open-water disposal can accommodate either
hydraulically or mechanically dredged material.
The levels of suspended solids in the water column around an open-water dis-
charge operation generally range from a few hundredths to a few tenths of a
part per thousand (p.p.t.). Concentrations are highest near the discharge
point and rapidly decrease with increasing distance down current from the
discharge point and laterally away from the plume centerline due to settling
and horizontal dispersion of the suspended solids. Concentrations also
decrease rapidly between each discrete hopper or barge discharge and after a
pipeline is shut down or moved to a new location. Under tidal conditions, the
plume will be subject to the tidal dynamics of the particular bay, estuary, or
river mouth where the discharge activity takes place.
One concern with open-water disposal is accurate placement of the contaminated
sediments and capping material. Bottom-dump barges (filled by a mechanical
dredge), followed by bottom-dump hopper dredges, can allow considerable point
accuracy and consolidation of material over conventional cutterhead pipeline
dredge and hopper dredge pump out discharges. There are, however, depth and
current limitations. These vary according to site conditions.
A submerged diffuser system (figure 3-2), originally designed by the U.S. Army
Corps of Engineers, is being field tested in the Netherlands. The diffuser is
designed to minimize water column turbidity by pipeline and hopper pump out
and allow equal or more accurate placement than the bottom-dump method and in
greater water depths. This system eliminates all interaction between the
slurry and upper water column by radially discharging the slurry parallel to
and just above the bottom at a low velocity. As presently designed, the
diffuser/barge system can be used in water depths up to 40 feet and can be
readily modified to discharge to 100 feet. Technology that could extend its
use to much greater depths is currently available.
3-4
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GAS VENT
DISCHARGE
DERRICK
WATER SURFACE
DREDGED
MATERIAL
SLURRY
VENT
>.'///>r;
FLUID MUD
MOUND
ANCHOR
PIVOT-BOOM \disCHARGE
SYSTEM BARGE x
SUBMERGED DIFFUSER
(POSITION AT THE BEGINNING OF
TIME PERIOD 4)
¦ ///77rr
BOTTOM SEDIMENT
MOUND PROFILE AT THE
END OF TIME PERIOD
Figure 3-2. Submerged Diffuser System
The diffuser (figure 3-3) reduces the velocity and turbulence associated with
the discharged slurry by routing the flow through a vertically oriented,
15-degree diffuser with a cross sectional area ratio of 4:1, followed by a
combined turning and radial diffuser section that increases the overall area
ratio to 16:1. The flow velocity of the slurry prior to discharge is reduced
by a factor of 16, yet the dredge's discharge rate (slurry flow velocity x
pipeline cross sectional area) is unaffected. The radial discharge area of
the diffuser can be adjusted and thus both thickness and velocity of the
discharged slurry can be controlled.
A discharge barge is used in conjunction with the diffuser to provide both
support and capability for lowering the diffuser to within 1 meter (m) of the
bottom at the beginning of the disposal operation and raising it as the fluid
mud accumulates. The barge also provides a platform for the diffuser while it
is being adjusted, serviced, or moved to a new site and can provide moorage
and pump out capabilities for clamshell barges and hopper dredges.
3-5
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,— MOUNTING FLANGE
SLURRY FLOW
CONICAL
DIFFUSER
SECTION
GAS VENT
7.5
TURNING AND RADIAL
DIFFUSER SECTION
GAS SHROUD
SUPPORT STRUT
RADIAL DISCHARGE
ABRASION PLATE
IMPINGMENT PLATE
777? 777? 7777 W 1777
BOTTOM SEDIMENT
Figure 3-3. Submerged Diffuser
Further discussion of capping and use of the submerged diffuser is contained
in chapter 4. The cost of using the submerged diffuser is discussed in
chapter 5.
a. General Site Criteria. An open-water disposal site for contaminated
sediments that are capped would be best located in a stable, low-energy area.
Generally, these areas lie below the active intertidal zone and preferably
be low the depth of storm wave influence. Ideally, the area should be under-
going net accretion. All of these factors contribute to long-term stability
of the cap and reduce convective forces that can increase loss of contaminants
through the cap. While the depth of the site is theoretically unlimited (by
use of vertical pipeline diffuser discussed earlier), experience with the
diffuser is minimal at this time. Other considerations that may require
detailed study include an assessment of resources at the site, geotechnical
data, and bottom currents.
Because the ideal open-water disposal site may not be available, its short-
comings may be somewhat relieved by use of the appropriate capping material.
The material should be able to resist erosion forces at the site. Grain size
should be similar to or coarser than the surrounding bottom sediment, at least
3-6
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sand or denser material. The cap can be gradually built up by hopper dredge
discharge as the dredge moves, thus "feathering" coarser materials onto finer,
contaminated sediments or directly placed by vertical pipeline diffuser.
Surface release is preferable for uncontained, mounded sediments; the vertical
pipe allows underwater diking (if needed) and rapid cap placement over sedi-
ments contained in a depression. Thickness of the cap will depend on specific
site conditions, including depth of potential bioturbation, mobility of con-
taminants, and current velocities, but a minimum of 3 feet is recommended.
b. General Designs. This report describes four general designs for
open-water sites (figures 3-4 to 3-7): deepwater mound, deepwater confined,
shallow water confined, and waterway confined. All of the designs have in
common the capping of the contaminated sediments placed at the site, with the
surface of the cap remaining aquatic. This is differentiated from nearshore
disposal where the final site elevation extends above high water.
One design not described here is a shallow water mound: this design was
eliminated from detailed consideration due to the relatively high energies
characteristic of shallow water environments. Although there may be specific
sites in shallow water environments that are quiescent enough to make mounding
viable, the construction considerations are virtually those of deepwater mound
with a thicker cap.
(1) Deep-water Mound. Deep-water mounding is the most simple design
evaluated (figure 3-4). Deep water is any depth below the influence of storm
waves, which will vary between sites. Theoretically, depths are unlimited,
although in fact the ability to accurately place contaminated and capping
materials establishes practical limits. Most deep-water sites would be
between 60 and 500 feet deep. Dredged material is transported to the identi-
fied disposal site and placed on the bottom by bottom dump or vertical pipe-
line diffuser. No attempt is made to "line" the bottom; that is, separate the
contaminated sediment placed from the existing substrate or to confine the
spread. However, the contaminated sediments should be concentrated as much as
possible in one location and partial containment may be possible by use of
natural depressions. Once the contaminated material is placed, it is capped
with clean, coarse material placed by any of the methods previously described.
Since the deep-water site was presumably selected for its low energy environ-
ment, a relatively thin cap (3 feet) should be sufficient depending on the
type of material used. As the contaminated material is mounded without con-
finement on the bottom, the major construction problem is to insure that
sufficient capping material is properly placed to completely cover the mounds
to sufficient depth (properly designed for the hydrodynamic regime and
bioturbation potential). So long as the cap remains in place, the major
pathways of concern for contaminant loss are soluble diffusion and convection
over time. Due to water depth, movement of ground water is expected to be
substantially absent and contaminant movement through the ground consequently
reduced.
3-7
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WATER SURFACE
DEPTH OF STORM
WAVE INFLUENCE
CONVECTION
SOLUBLE
DIFFUSION ^
CONVECTION
BOTTOM V
CURRENTS
BIOTURBATION
CONTAMINATED
SEDIMENT
SOLUBLE
nicti iciriki"^
EXISTING
BOTTOM
3 FOOT CAP
OF CLEAN
SEDIMENTS
CONVECTION
Figure 3-4: Deep-Water Mound
3-8
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WATER
SURFACE
DEPTH OF STORM
WAVE INFLUENCE
60-500+
FEET
SOLUBLE
DIFFUSION,
CONVECTION
BIOTURBATION
EXISTING
BOTTOM
3 FT. CAP OF CLEAN SEDIMENTS
CONTAMINATED
SEDIMENTS
UNDERWATER
DIKE
SOLUBLE
DIFFUSION,
CONVECTION
NATURAL OR
EXCAVATED
DEPRESSION
Figure 3-5: Deep-Water Confined
3-9
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UPLAND
WATER
SURFACE
HIGH TIDE
LOW TIDE
10-60 FEET
BIOTURBATION
DEPTH OF
STORM WAVE
INFLUENCE
+ 6 FEET CAP
DIKE
CONTAMINATED
SEDIMENTS
EXISTING
bottom
Figure 3-6: Shallow-Water Confined
3-10
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UPLAND
WATER
SURFACE
HIGH TIDE
LOW TIDE
15-50 FEET
SOLUBLE
DIFFUSION,
CONVECTION
CAP (3-6 FEET)
EXISTING
BOTTOM
CONTAMINATED
SEDIMENT
GROUND
WATER
SOLUBLE
DIFFUSION,
CONVECTION
Figure 3-7: Waterway Confined
3-11
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(2) Deep-water Confined. This design differs from deep-water mound-
ing in that materials are placed in a natural or manmade depression in the sea
floor to aid confinement (figure 3-5). Use of a vertical pipe allows con-
struction of underwater diking to encircle the site or work in combination
with existing natural features (e.g., rock outcrop). This design is more
expensive than deep-water mounding due to site preparation, but may be easier
to cap and the contaminated sediments are more "isolated" from the aquatic
environment. Just as with the deep-water mound, the stable, low energy
environment allows for a relatively thin cap. Pathways for contaminants to
escape are essentially the same as for the deep-water mound.
(3) Shallow-water Confined. Shallow-water areas are those within the
influence of storm waves but below intertidal elevations. Hence, final eleva-
tion of the cap would be within the -10 feet MLLW to -60 feet MLLW range. As
with deep-water confined, this design (figure 3-6) includes manmade contain-
ment structures or excavation, wholely or in combination with existing natural
features, to hold the contaminated sediments. Because of higher energies
found in shallow-water areas, a thicker cap is necessary (e.g., 6 feet rather
than 3 feet) for this design. In addition, burial of the cap beneath a
buffering layer of clean sediment similar to the surrounding substrate may be
appropriate in some instances to protect the integrity of the cap from erosion
and bioturbation and to mitigate esthetic and resource impacts. Pathways for
escape of contaminants are increased over deep-water designs by tidal or
current induced convection of soluble fractions. Bioturbation and leaching
into the underlying substrata are of more concern in the shallow-water environ-
ment than in deep-water. Ground water infiltration from adjacent uplands may
also be of concern. The increased cost of site preparation may be partially
or completely offset by savings in transportation cost to a deep-wate? site.
(4) Waterway Confined. Although this design (figure 3-7) is very
similar to the option of burial of sediments in shallow-water areas, it
differs in one very important respect. The shallow-water confined design can
apply to many different geographic locations: open water, aquatic shelves
near an urban shoreline, or relatively pristine environments. In these
environments, agitation by currents, tides, and storms are factors that must
be countered by the site design (i.e., a thicker cap, a buffer over the cap,
frequent cap maintenance). In the waterway design, a confined pit is excavated
deep within and into the bottom of an existing waterway. Preferably, the dis-
posal site should be located in an area that will not be dredged. Otherwise
the disposal pit must be of sufficient depth to be well below anticipated
dredging depths. This pit may be lined (Rotterdam-Putten Plan, see appendix
2a) or not, but the contaminated sediments from elsewhere in that waterway or
harbor are placed in the excavated pit, the pit capped, and some of the
excavated material replaced over this cell of contaminated material to about
the original bottom contour. Hydraulic energies associated with the Commence-
ment Bay waterways are much less than other shallow water environments, in
addition, because existing sediments in Commencement Bay waterways show
relatively high levels of contaminants, other contaminated material placed in
the confined pit would be generally similar to the surrounding material. This
would substantially reduce the concern associated with leaching of contami-
nants to underlying substrates. Escape pathways are virtually identical to
shallow-water confined, though reduced in intensity to levels similar to the
deep-water designs.
3-12
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3.03.02 Upland Disposal. Upland disposal involves the placement of dredged
material in environments not inundated by tidal waters (figure 3-8). Upland
disposal sites are normally diked, confined areas that retain the dredged
solids while allowing the carrier water to be released, and as such are most
often associated with hydraulic dredges (pipeline or hopper with pump out
capability). Upland sites can also accept dredged material that has been
dewatered elsewhere and transported in by truck or rail (if hydraulically
dredged) or has simply been loaded directly into trucks or railcars by
mechanical dredges. Upland disposal sites may be located immediately adjacent
to, or removed great distances from, the dredging site.
As nearly all upland disposal sites are diked areas, the major components of a
containment area are shown schematically in figure 3-9. The two objectives
inherent in design and operation of containment areas are to provide adequate
storage capacity to meet the dredging requirements and to attain the highest
possible efficiency in retaining solids during the dredging operation. Basic
guidelines for design, operations, and management of containment areas are
presented by Palermo, et al. (1978) and Montgomery, et al. (1983).
Behavior of hydraulically dredged material discharged into a containment site
has been generally described in section 3.02. The effluent is discharged from
the containment site over a weir. This effluent is normally characterized by
its suspended solids concentration and rate of outflow. Flow over the weir is
controlled by the static head and the effective weir length provided. To
promote sedimentation, the inflow slurry is encouraged to pond; a minimum
ponding depth of 2 feet is recommended for a continuous disposal activity.
Ponding depths less than 2 feet may be acceptable if the dredging occurs
intermittently. The depth of pond water is controlled by elevation of the
weir crest. Minimum freeboard requirements and mounding of coarse-grained
material result in a ponded surface area that is smaller than the total sur-
face area enclosed by the dikes. Dead spots in corners and other hydraulically
inactive zones further reduce the effective surface area, where sedimentation
occurs, to considerably less than the ponded surface area. Spur dikes (inter-
nal dikes) can be used to improve settling efficiency by modifying flow
patterns through the site, modifying currents, and allowing more time for
settlement (figure 3-10).
Several expedient measures can be employed to enhance retention of the sus-
pended solids within a containment area of a given size before effluent dis-
charge to receiving waters. They include: intermittent pumping, increasing
the depth of ponded water, increasing the effective length of the weir,
temporarily discontinuing operations, or decreasing the size of the dredge.
a. General Site Criteria. Normally, upland site criteria are related to
the method of dredging employed and the volume of material dredged. Specific
site criteria for selection and evaluation of potential upland disposal sites
in the Commencement Bay area were developed for this report. These criteria
and their application are explained in section 3.05 and generally relate to
site size (which affects its capacity), distance from the harbor area where
most contaminated sediments are expected to originate, site elevation, and
3-13
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VOLATILIZATION
DIFFUSION
CAPILLARY
MOVEMENT
PRECIPITATION
BIOTURBATION
c=l
CAP (3-6 FEET)
C3
a
EXISTING
UPLAND
SURFACE
INFILTRATION
DIKE
DIKE
CONTAMINATED
SEDIMENTS
LEACHATE
GROUNO WATER LEVEL
Figure 3-8: Upland Disposal
3-14
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MOUNDED COARSE-GRAINED
DREDGED MATERIAL
DEAD ZONE
INFLUENT
'-:v:
AREA FOR SEDIMENTATION
Z&g -
DEAD ZONE
WEIR
ZZ3
:>
EFFLUENT
PLAN
INFLUENT
AREA FOR SEDIMENTATION
PONDING
DEPTH
COARSE-GRAINED
DREDGED MATERIAL
FREEBOARD
WEIR
AREA FOR FINE-GRAINED EFFLUENT
DREDGED MATERIAL STORAGE
CROSS SECTION
Figure 3-9: Conceptual Diagram of a Confined
Dredged Material Disposal Site
3-15
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I
T
I
A. LONGITUDINAL
SPUR DIKES
B. TRANSVERSE *
SPUR DIKES
C. COMBINATION SPUR DIKES
FOR DIFFICULT ACCESS
AND SHAPE RESTRICTIONS
Figure 3-10: Examples of Longitudinal and Transverse Spur
Dike Configurations
3-16
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amount and cost of site preparation. Beyond these generic considerations>
final site selection criteria will depend on answers to a number of environ-
mental and engineering concerns. Hydrologic conditions, including the
presence, depth, extent, and use of ground water, will be critical in all
cases. Of equal concern and related to ground water is site foundation
(geology, soils, etc.) and the presence of hazardous materials onsite that
will require identification and removal prior to site use. Many of the other
information needs described for selection of open-water disposal sites apply
to upland sites as well.
b. General Designs. The design of most upland disposal sites is
similar. In most cases, earthen dikes are constructed to enclose the site.
In some instances, however, the site may be partially or entirely excavated;
although excavation is typically much more expensive than dike construction,
especially where large acreages are involved as is the case in Commencement
Bay. Because of this, excavation was not considered in this report. The only
consideration not common to diking and excavation is dike failure; however,
proper design eliminates this as an important problem.
3.03.03 Nearshore Disposal. Nearshore disposal is distinguished from both
open-water and upland disposal methods by placement of the dredged material in
an aquatic environment (normally marine and tidal) but the final elevation
after filling is above water (figure 3-11). Nearshore disposal sites for
contaminated sediments are always diked, confined areas. These sites normally
are used in association with hydraulic dredges but can accommodate dredged
material from mechanical dredges directly, bottom-dump barges, and direct
dumping from trucks and/or railcars.
General site criteria and information needs are identical to upland disposal
and include, in addition, the water exchange and movement concerns of shallow
water confined designs. Designs most frequently involve diking of old harbor
waterways that are no longer actively used. Nearshore excavation is possible,
although normally too expensive for consideration. One site exists in
Commencement Bay that originally was excavated and used as a graving dock.
Such opportunities are rare.
3.04 Contaminant Efficiency of Disposal Methods, The evaluation of contami-
nant behavior during dredging that is contained in chapter 2 carries over to
disposal, especially for pipeline dredging. For purposes of this report,
disposal of mechanically dredged sediments begins at the time sediments are
placed in the barge, truck, or railcar and includes their transportation to,
as well as the actual discharge at, the disposal site. With hydraulic
dredges, dredging and discharge are all part of a single, extended process.
The contaminant evaluation for this disposal chapter will cover the time
following discharge of the slurried sediments into a contained upland or
nearshore site or into an aquatic site.
3.04.01 General. The properties of a dredged sediment, and the short- and
long-term physical and chemical environment of the dredged material at the
3-17
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UPLAND
VOLATILIZATION
PRECIPITATION
GROUND
WATER
Ik
BIOTURBATION
CAP (3-6 FEET) ~
<*Q7-INFILTRATI0N
^/cONTAMINAT5D»^
UNSATURATED^/ CONTAMINATE
SATURATED ^ySEDIMENTS
0
"Or
LEACMATE
DIKE
SOLUBLE
. CONVECTION
J\ VIA TIDAL
y PUMPING
HIGH TIDE ¦
SEEPAGE
K SOLUBLE
) DIFFUSION,
V SEEPAGE
EXISTING
BOTTOM
Figure 3-11. Nearshore Disposal
disposal site, influences the fate and environmental consequences of contam-
inants. The processes involved with release or immobilization of most sedi-
ment-associated contaminants are regulated to a large extent by the physical-
chemical environment at the disposal site. The major parameters that
influence contaminant behavior in dredged material are the amount and type of
clay; organic matter content; amount and type of cations and anions associated
with the sediment; the amount of potentially reactive iron and manganese; and
the oxidation-reduction, pH, and salinity conditions of the sediment.
Although each of these sediment properties is important, much concerning the
release of contaminants from sediments can be inferred from the clay and
organic matter content, initial and final pH, and oxidation-reduction condi-
tions. Much dredged material is high in organic matter and clay and is both
biologically and chemically active. It is usually devoid of oxygen and may
contain appreciable sulfide. These sediment conditions favor effective reten-
tion of many contaminants, provided the dredged materials are not subject to
mixing, resuspension, or changes to their chemical environment. Sandy sedi-
ments low in organic matter content are much less effective in retaining metal
3-18
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and organic contaminants. However, sandy sediments tend not to accumulate
contaminants unless a contamination source is nearby. Should contamination of
these sediments occur, potentially toxic substances may be readily released
upon mixing in a water column or by leaching (USACE, 1983b).
Many contaminated sediments are in a reduced state and at near neutral pH
(7.0), initially. Disposal into quiescent waters maintains anaerobic condi-
tions and favors contaminant retention. Certain sediments that are non-
calcareous and contain appreciable reactive iron and, particularly, reduced
sulfur compounds, can become moderately to strongly acid as result of drying
and subsequent oxidation. These conditions occur in upland disposal sites and
in the upper, unsaturated layers of nearshore disposal sites. This altered
environment greatly increases the potential for the release of heavy toxic
metals. In addition to the effects of pH changes, the release of most heavy
metals is influenced by oxidation-reduction conditions. Thus, sediments which
tend to become strongly acid upon drainage and long-term oxidation may pose a
high environmental risk (USACE, 1983b).
Mobility implies a quantifiable rate process and is a function of the chemical
species, the solvent (water), the type of soil/sediment matrix, the physical
state of the system, chemical concentration levels, and certain geometric
factors. These factors are discussed by Thibodeaux (1984) (appendix 2a).
There are several physical, chemical, and biological processes that can result
in transport of contaminants through a sediment/water environment. These
mechanisms include the following:
o Diffusion of dissolved chemical species down a chemical concentration
gradient and through the sediment-water interface.
o Convection and dispersion of dissolved chemical species (and fines) due
to water flow through the sediment (ground water, precipitation, runoff, tidal
action) and sediment consolidation.
o Bioturbation of the sediment.
o Scour and suspension of surface sediment particles by bottom water
currents.
o Gas generation and ebullition within and through the sediment/water
interface.
3.04.02. Volatile Phase Contaminants. To a limited extent, the loss of
volatile contaminants during disposal will depend on the dredging technique
and controls employed. Conditions and concerns of mechanical versus hydraulic
dredging are contained in chapter 2; these are most important for volatile
contaminant release in the short term, during or immediately following dis-
charge. Once the contaminated sediments have been placed in the disposal
sites and capped, the number and strength of contaminant transport mechanisms
3-19
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operating on the material become more important factors. For example, mechan-
ically dredged material contains less in situ water than does pipeline slurry.
The water contained in the dredged slurry acts as its own transportation
medium to spread the sediment through the disposal site and at the same time
provides a buffer reducing the sediment's exposure to air. For volatile
contaminants, this aids retention. Mechanically, and occasionally
hydraulically, dredged material may require reworking with a bulldozer in
upland and some nearshore disposal sites, an operation that increases the
opportunity for loss of volatile contaminants.
a. Open-Water Disposal. Transport by hydraulic pipeline is covered as a
part of dredging. A general description of transportation concerns for
mechanical dredging is included in section 3.02. Because of the exposure time
to air that occurs with mechanically dredged sediments in barges, some loss of
volatile contaminants will occur during transportation of the material to the
disposal site. Once placed in an open-water site and capped, escape will be
limited to minor gas diffusion through the cap and bioturbation. The rate of
loss can be controlled by maintenance of the cap's integrity. Due to the
anaerobic conditions of the subaquatic environment, volatile mobility will
likely be an order of magnitude below upland or nearshore disposal.
b. Upland Disposal. If the material has been mechanically dredged, some
loss of volatile contaminants will have occurred during transport to the
site. No dewatering of the material will be necessary. Hydraulic placement
of sediments results in loss of volatiles in proportion to their exposure to
air. Submerging the pipeline outlet and not allowing a splash or "glory hole"
to develop aids retention of volatiles. A fraction of the volatiles will be
lost into the atmosphere as the slurry moves through the site. After the
dredged sediments have settled out and the site is capped, volatile contami-
nant mobility continues via diffusion, air convection over and through the
caps, and possibly barometric pressure pumping. Capping material and thick-
ness will control the rate of release. As the sediment dewaters, volatiles
that are soluble or sediment bound in the presense of water may be released.
c. Nearshore Disposal. Loss of volatile contaminants from use of a
nearshore disposal site is substantially the same as upland disposal, with the
exception that not all of the contaminated sediments will become unsaturated.
Submerging the pipeline outlet in the disposal site would be easier to do at a
nearshore site than an upland site. Overall, rate of loss would approximate
that of upland disposal.
3.04.03 Soluble Phase Contaminants. Nearly all chemical contaminants are
soluble to some degree and can be found in association with all three phases
of the sediment (gas, liquid, and solids). In terms of their affinity for
going into solution, they can be characterized as highly soluble (will easily
exchange from one phase to another) or slightly soluble (will not easily
exchange or require special conditions). This degree of solubility depends on
a variety of factors and can change as specific conditions are altered by the
act of dredging, during transport of the dredged material, during its dis-
charge into the disposal site, and following its disposal and capping. The
3-20
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first three actions occur during a very short time frame and their influence
°n contaminant mobility is relatively instantaneous with regard to evaluating
disposal methods. The long-term condition changes and effects on contaminant
phase, particularly with regard to solubility, are of greater concern and
complexity.
A percentage of the potentially soluble contaminant fraction will be in
solution in the interstitial water of the sediment. The remainder will still
be bound to sediment particles. In this way, an equilibrium exists on a small
8cale, with the fraction of chemical contaminant potentially available for
short-term release during dredging or disposal operations approximating the
interstitial water concentrations and the loosely bound fraction in the
sediments (chapter 2.0). Hydraulic dredging, by more thoroughly agitating the
sediments, releases more of the interstitial water from the sediments and
allows new water to contact the sediment bound fractions. This increases the
propensity for any loosely bound fractions to exchange, but provides greater
dilution of the contaminant laden water than does mechanical dredging. The
greater efficiency of hydraulic suction removes contaminated interstitial
water from the dredging site along with the slurried sediments, and the issue
is transferred to disposal. Mechanical dredges release less of the inter-
stitial water overall than do hydraulic dredges. If a watertight bucket is
used, only at the edges of the dredge cut is interstitial water immediately
lost. Thus, a smaller volume of sediment is exposed to new water and exchange
potential. Most of the sediment and interstitial water dredged by a water-
tight bucket remain consolidated as they are placed into the barge, truck, or
railcar for transport to the disposal site. Some of the interstitial water
will drain from the sediments during transport and will be lost to the sur-
rounding environment (if the container is not watertight) or will be lost or
•nay require treatment at the disposal site (if the container is watertight).
These are short-term releases.
Once deposited at the disposal site and capped, the concern for retaining
soluble contaminants becomes complex. Contaminant fractions that were tightly
bound to the sediment particles can, over time and due to altering conditions,
become more prone to go into solution. This is especially true for heavy
metals when placed in upland disposal sites. Under saturated conditions, many
metals remain tightly bound to the sediments. In unsaturated conditions,
where oxidation can occur, these contaminants can become highly soluble and
readily leach to surface runoff or ground water percolating through the
material. Changes in pH have similar implications for other compounds.
Therefore, long-term releases of soluble fractions have greater and less
understood potential for adverse effects.
a. Open-Water Pisposal. Whether hydraulically or mechanically dredged,
those soluble fractions released in the short term will be lost in the
receiving waters. This will occur immediately upon discharge and continue
until the disposal site is capped, although at a much slower rate once the
material has come to rest. Immediately following capping and for an indeter-
minate transient period, no contaminants will be released, being encased by
the cap and the sides and bottom of the disposal site. Over time, aided by
3-21
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diffusion and convection through the cap, soluble contaminants will begin to
migrate into the clean cap material. Ultimately, these contaminants will
saturate the cap material, decreasing in concentration level as they move
through the cap, and be released into the overlying water column. Because
physical, chemical, and biological conditions are relatively stable at deep-
water sites, soluble contaminant loss would be gradual and the volume of
overlying water offers substantial dilution. A management technique to
further delay this long-term release is to add more capping material. Some
migration of contaminants into interstitial water of underlying sediments
through diffusion is also possible. Bioturbation is another source of
contaminant release. Maintenance of the integrity of the cap is the maximum
control.
b. Upland Disposal. Placement of contaminated sediments in an upland
disposal site by hydraulic dredge would produce a large quantity of water
containing soluble contaminants extracted and diluted from the sediments.
Depending upon the types of chemicals released, treatment of this water prior
to discharge back to the aquatic environment may be necessary. Mechanically
dredged material will have less water to treat, if treatment is necessary,
though contaminant concentrations are likely to be higher in this water. By
use of upland disposal, soluble contaminants from this short-term release can
be controlled and treated rather than lost. However, over time this environ-
ment is less stable than is the open-water environment. As the sediments
drain, physical and chemical conditions change and affect the stability of
some contaminants, causing them to go into solution. The cap can be designed
to retard volatilization and precipitation entry, but seepage into and out of
the site will allow contaminants to escape. Lining would retard soluble con-
taminant escape, but not totally eliminate it in the long term. Leaching into
ground water is a major concern. However, just as upland disposal sites offer
the greatest control possibilities for the effluent, they offer the greatest
opportunity for controlling and treating (as necesary) the release of soluble
contaminants over the long term. Further discussion is provided in chapter 4.
c. Nearshore Disposal. In comparison to upland disposal, nearshore
disposal possesses many of the same concerns for soluble contaminants,
although fewer opportunities for control exist (see chapter 4). In the short
term, control and treatment of the contaminant laden effluent from either
hydraulic or mechanical dredging is possible. Once filled and capped, the
upper layers of contaminated sediment will drain until two distinct levels
form. The lower level of sediment will continue to be saturated as a result
of precipitation and ground water infiltration as well as marine water
intrusion. Soluble contaminants will release through diffusion and convection
as a result of tidal pumping and seepage. The upper sediment layer will drain
over time and carry soluble contaminants into the lower, saturated sediments.
As the upper layer of material becomes more "upland," long-term releases of
contaminants due to changes in the physical and chemical equilibrium are
predictably similar to what would occur in a completely upland site. However,
control of these long-term releases is substantially more difficult at a
nearshore than at an upland location. Additionally, it is inevitable that
much of the soluble contaminant fractions will get back into the marine
3-22
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environment by diffusion and convection through and around the containment
dike. One estimate is that most soluble contaminants would be lost from this
type of site in one to two decades, if no control measures are used. The
potential for adverse effects is greater in the nearshore than at an open-
water location due to proximity to human activity and greater biological
produc tion.
3.04.04 Sediment-Bound Contaminants. These contaminants, especially those
that are tightly bound, are relatively easy to handle. Removal of the sedi-
ments and solids (via dredging) removes the contaminants (chapter 2); disposal
and confinement of the sediments confines the contaminants. Control of solids
(especially fines and organic compounds) to maximize retention in the disposal
area, and completely and sufficiently capping the site to prevent particle
migration, solves the disposal problem. However, sediment-bound contaminants
may change their binding over time as chemical and physical characteristics of
the disposal site change.
a. Open-Water Disposal. Loss of sediment from the disposal site during
placement of the contaminated material is the primary source of short-term
release. As many contaminants are bound to the finer-grained sediments and
these components are most easily lost during discharge, some release is
inevitable. Discharge into quiet waters will minimize resuspension by
currents and allow more rapid settling out of fines. Once the contaminated
material is capped, maintaining the cap's integrity against erosion and
bioturbation is sufficient to retain sediment-bound contaminants.
b. Upland Disposal. As with open-water disposal, the primary concern is
control of solids. Mechanical dredging and direct placement of the sediments
in the disposal site maximizes retention. For hydraulically dredged material,
proper design of the disposal site and weir, including spur dikes, is impor-
tant. The opportunity to further treat the effluent, including flocculation,
makes this disposal method highly effective for solids. The principal loss of
sediment-bound contaminants results from changes to physical and chemical
parameters that cause sediment-bound contaminants to go into solution. Short
of this phenomenon, minor leakage of sediment through the cap, dikes, or
liners allowing release of contaminants is possible in some instances.
Bioturbation and erosion represent the greatest source of solids loss.
c. Nearshore Disposal. This method has the same concerns and opportuni-
ties as upland disposal for the retention of sediment bound contaminants.
Solids leakage through dikes must be routinely considered.
3.05 Disposal Sites. One of the tasks undertaken for this report was the
identification and evaluation of potential disposal sites that could accept
contaminated sediments from Commencement Bay. Selection of individual sites
for further evaluation was based on criteria explained below. These sites are
shown on plate 2.
The primary consideration was to locate potential disposal sites in proximity
to the Commencement Bay Nearshore/Tideflats Superfund Site and ongoing or pro-
posed navigation dredging areas. Thus, no sites outside of the Commencement
-------
Bay area were identified for evaluation; off-site considerations and options
are discussed briefly following the descriptions and evaluations of specific
disposal sites.
The identification of sites was not exhaustive. The objective of the exercise
was to determine, generally, whether capacity existed within a least cost,
least disturbance, reconnaissance level of detail to accommodate the large
volumes of contaminated sediments anticipated. To this end, a number of
potential disposal sites for each disposal method were identified, resulting
in a total capacity that is expected to exceed actual needs. Those sites that
did not pass the initial screening criteria or are not recommended here should
not be considered unacceptable for potential consideration; they are simply
unnecessary or less desirable at this time.
3.05.01 Site Selection Criteria. Table 3-1 shows the criteria that were used
to identify potential disposal sites for the three disposal methods discussed
in the previous sections of this chapter. These criteria were selected based
primarily on cost and equipment limitations.
TABLE 3-1
Disposal Method
Open-Water
Upland
Nearshore
INITIAL SITE SELECTION CRITERIA
Disposal Criteria
Distance: within 12 miles of waterways
Distance: within 2 miles of waterways
Capacity:.?./ greater than 50,000 c.y. (sites below
+20 feet MLLW)
greater than 1,000,000 c.y. (sites at
or above +20 feet MLLW)
Other: absence of permanent development
Distance: within 12 miles of waterways
Elevation: -35 feet to +20 feet MLLW
Capacity: greater than 100,000 c.y.
1/Sites would be filled to either +20 feet MLLW or +35 feet MLLW.
Distance criteria were based on equipment limitations and cost considera-
tions. It was assumed that large cutterhead pipeline dredges (22- to 36-inch)
were the most likely candidates for hydraulic dredging. Dredges of this size
would be able to pump typical Commencement Bay sediments about 2 miles on the
level before a booster pump would be required. This distance is approximate
and must be modified by elevation considerations. Thus, the hills to the
north and south of Commencement Bay represent a limit to pipeline transport.
The 12-mile distance criterion was selected as the farthest distance that a
3-24
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two-barge mechanical dredging operation can continuously accommodate (i.e.,
the dredge will fill one barge while the second is proceeding to the disposal
site, dumping, and returning). Beyond 12 miles a three-barge operation would
be necessary. In both cases, hydraulic or mechanical, adding booster pumps or
another barge increases costs.
The distance criteria also relate directly to the elevation criteria, espe-
cially for consideration of upland sites. Filling of upland sites to +20 feet
MLLW and to +35 feet MLLW were considered. For small sites (less than 40
acres and with less than 1 million c.y. capacity) final site elevation would
be +20 feet MLLW. Filling above that elevation would remove the parcel from
railroad access and could cause land use changes (e.g., change heavy industrial
to light industrial use). Fill of one or more large sites to the maximum
economical pumping height of +35 feet MLLW might provide bay-wide benefits to
justify the tradeoff. For nearshore disposal, filling a site above +20 feet
MLLW removes it from easy water access and reduce the site's potential for
development.
Minimum site capacity was determined partially based on cost considerations.
Although actual costs must be determined on a case-by-case basis, a site with
at least 100,000 c.y. capacity would be of sufficient size to amortize
development costs for treatment facilities and site preparation costs, and
would provide sufficient area (about 40 acres) to encourage settling of
solids. It was felt that larger sites of at least 1 million c.y. capacity
represent long-term, multiple-use disposal opportunities rather than one-time
uses. This opportunity for repeated use over time would imply a displacement,
either potential or actual, of heavy industrial use of the site. Capacity for
accepting at least 1 million c.y. of contaminated sediment has tangible
economic inducements for long-range solutions to Commencement Bay Superfund
and navigation issues.
Only sites that had no large-scale, permanent development or facilities in
place were considered.
3.05.02 Open-Water Disposal Sites. Historically, there have been many
unconfined, open-water disposal sites in Commencement Bay. While past studies
have identified many of these former sites, an unknown number have never been
identified (often one- or two-time occurrences that were never reported).
This report considers three open-water sites located in Commencement Bay
(figure 3-12). A brief description of each site is provided including a
limited evaluation of the site's strengths and weaknesses. Acquisition costs
for these sites were not investigated.
a. Puyallup River Delta Disposal Site.
(1) Description. This site is located 1/2-mile west of the mouth of
the Puyallup River at latitude 47° ,16 1 ,30" , longitude 122° ,26' ,00". Until
1972, it was the Department of Natural Resource's (DNR) designated open-water
site; ownership remains with the State of Washington. The site occupies the
3-25
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Puyallup River delta; surface radius of the former disposal site is 900 feet.
Bottom elevation slopes from -28 feet MLLW to approximately -200 feet MLLW.
(2) Limitations. The site has a history of major slides from the
delta into the deep water of Commencement Bay on about a 10-year frequency.
Disposal of fine-grained sediments typical for Commencement Ray will increase
the frequency of slides. Capping would be difficult and slides could re-expose
the contaminated material. Because the area is active, benthic communities
would be short lived. However, it is located within the migratory paths of
salmonids moving to and from the Puyallup River system; and Indian commercial
net fishing occurs. Disposal may have to avoid times when juvenile salmonids
are present and special restrictions may be necessary during the fishing
season. Because of its location on the delta, a large volume of uncontami-
nated material is available nearby at very low cost (dredging) which could be
used to cap contaminated sediments. It may be possible to place the con-
taminated sediments at the edge of the slide zone where the continuing
accretion could further bury them.
(3) Information Needs. Detailed geotechnical evaluations and
environmental characterizations are necessary.
b. Department of Natural Resources (DNR) Disposal Site.
(1) Description. The site has been the DNR designated open-water
site for Commencement Bay since 1972 ; it is located at latitude 47°, 17',40"
and longitude 122° ,27' ,35", over 3 miles from the anticipated dredging
sites. Surface radius of the site is 900 feet; depths are in excess of
500 feet. Bottom topography is nearly level. The site has been used
regularly for dredged material disposal since its designation and is known to
be contaminated by a variety of compounds.
(2) Limi tations. The depth would make accurate placement of the
contaminated material and cap within the limits of the designated area diffi-
cult. Monitoring would be similarly difficult. However, the site has the
capacity to receive all acceptable dredged materials projected for the future
of Commencement Bay. Since the site has been used regularly in the past,
contaminant levels at the site are higher than background levels. Therefore,
disposal of contaminated material at the DNR site may be expected to have a
lesser biological impact than would disposal of contaminated material at an
uncontaminated area. Also, the site's depth places it outside the feeding
depths of salmonids and many commercial fishes.
(3) Information Needs. Bottom current energies should be defined.
Limited geotechnical and environmental characterization may be needed. This
site would require the least amount of new information for open-water sites.
c* Hylebos/Browns Point Disposal Site.
(1) Description. This site is located midway between the mouth of
Hylebos Waterway and Browns Point at latitude 47°, 17*,40", longitude
3-26
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|lv£A\\\ j W
. Meekejf
Browns Point
•vVsW • i •
Browns Point
-300^
D.N.R. DISPOSAL SITE
HYLEBOS/BROWNS POINT
DISPOSAL SITE
%f> Light
Grain
Elevators
PUYALLUP RIVER DELTA
DISPOSAL SITE
Wrigtl*
Smwiini
SCALE 1:24000
FIGURE 3-12: POTENTIAL OPEN-WATER DISPOSAL SITES
3-27 IN COMMENCEMENT BAY, WASHINGTON
-------
122° ,25 ' ,30". Depths range between 100 and 200 feet. The site is a
natural, horseshoe-shaped depression; closing the fourth side with an under-
water dike would provide capacity for over 2.5 million c.y. The site is
within 2 miles of Hylebos, Blair, and Sitcum Waterways. Ownership is by the
State of Washington.
(2) Limitations. Relatively little is known of the site, so exten-
sive investigations may be required. Local fishermen indicate that the area
is popular for bottom fishing though success is unknown. While the depth is
outside the normal feeding range of salmonids, the Puyallup Tribe indicate
that the upper water column is seasonally used by drift netters. As the site
has not been previously used for disposal, aquatic resources may be undis-
turbed and possibly significant; use of the site would adversely affect these
resources. However, past and present use of the water surface for extensive
log booming may have affected the benthic community. Capacity of the site
(2.5 million c.y.) is sufficient for many years of disposal, allowing incre-
mental diking. Diking the open, fourth end would allow more complete contain-
ment of contaminated materials. This and the lesser depth (100 to 200 feet)
would make capping and monitoring easier than at the existing DNR open-water
s i te.
(3) Information Needs. As noted, least is known of this site. The
site may be environmentally significant. Detailed investigations of all
considerations (geotechnical , hydrology, environment) would be necessary.
3.05.03 Upland Sites. Seven upland sites located in the Commencement Bay
area (figure 3-13) were considered. Site acquisition costs were not investi-
gated. A brief description of each site is provided, including a limited
evaluation of the site's strengths and weaknesses. Port of Tacoma Site No. 5,
shown on the figure, has since undergone use for other purposes and it is not
discussed here.
Concerns about upland disposal have been expressed by several entities. The
Puyallup Tribe is concerned about the potential disposal of any contaminated
materials within the boundaries of their reservation. The Tacoma/Pierce
County Department of Public Health has questions about the effects that upland
disposal of contaminated dredged material may have on ground water and drain-
age systems and the possible burial of hazardous materials already existing on
the site. The Port of Tacoma is concerned about the loss of real estate
potential should sites be filled above the normal industrial grade elevation
(+20 feet HLLW); and the port's leasees may express concerns about locating on
or near contaminated materials.
a. Puyallup Mitigation Site.
(1) Description. This site is located north of the Puyallup River
and east of Lincoln Avenue, approximately 1 mile from Sitcum and Milwaukee
Waterways, and 2 miles from the middle of Blair Waterway. Ownership is by the
Port of Tacoma. The 40-acre site has been previously filled with dredged
material and its current elevation is approximately +18 feet MLLW. Filling to
3-28
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+35 feet MLLW is contemplated; this would provide about 1 million c.y. capa-
city. Vegetation has reestablished, otherwise the site is vacant. The exist-
ing fill could be used to construct containment dikes. The site is currently
zoned S-10 (Port Industrial) by the city of Tacoma; however, it has been
proposed as a wetland creation site by the port as mitigation for filling of
site No. 5 for the Sea-Land terminal development (see figure 3-13). Slurry
water from this site would be discharged into the Puyallup River.
(2) Limitations. Presently, this site is proposed as mitigation by
excavating the site and breaching the Puyallup River dike to create freshwater
wetlands. Presumably an alternative mitigation site would need to be located.
(3) Information Needs. At least general geotechnical and environ-
mental information are or will be available due to the ongoing discussions on
use of the site as a mitigation area. Detailed hydrologic studies may be
necessary to determine potential ground water effects.
b. Port of Tacoma Site "D".
(1) Description. This 60-acre site is bounded by the Port of Tacoma
Road on the northeast, the Union Pacific Railroad (UPRR) switchyard on the
southeast, and Marshall Way on the northwest, within the area commonly known
as the "Tacoma Tideflats." The site is a former dredged material disposal
area and has been filled to approximately +16 feet MLLW. Filling of the site
to +20 feet MLLW provides capacity of 100,000 c.y.; fill to +35 feet MLLW
provides capacity of an additional 1,450,000 c.y. (total: 1,550,000 c.y.).
The site is centrally located and within 1 mile from Hylebos, Blair, and
Sitcum Waterways. Ownership is by the Port of Tacoma. The site is zoned S-10
(Port Industrial) by the city of Tacoma. The discharge path for this site is
into the lower end of the Blair Waterway through an existing drainage canal.
(2) Limitations. The port has no current plans for developing the
site and no prospective tenant, suggesting that the site may be available.
Because the site has been filled in the recent past, its environmental value
is judged relatively low.
(3) Information Needs. Because of its history of fill, detailed
environmental investigations are probably unnecessary. Hydrologic and limited
geotechnical information to determine potential ground water effects would be
prudent.
c* Puyallup River/Railroad Site.
(1) Description. This site is located on the south side of Inter-
state 5 (1-5), upstream from the I-5/Puyallup River bridge, and is situated
between the UPRR and the Puyallup River. It is approximately 2 miles from the
heads of Blair and Hylebos Waterways. Present elevation is approximately +9
feet MLLW. Filling the +80-acre site to +20 feet MLLW provides capacity of
1.3 million c.y.; filling the site to +35 feet MLLW provides capacity for an
additional 2 million c.y. (total: 3.3 million c.y.). One-third of the site
3-29
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Pj \\ jiy - IJI. c
s\ t=\L!MU-&U
wm** *
PORT OF TACOMA
DISPOSAL SITE #5
I" m II v 1
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mm
/ ;
1 | f'S - «
, !X ^ f'^tr """""A— - " H'ui T\ J
\ \ V^TPUYALLUP «/¦*
MITIGATION
.$ DISPOSAL SITE \ r I'!-
-/x v> ^ /
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:•= '• *
&
II
a i- H
* *
Tr ^
rip ,<*
i VT
f
Y
V* ' / • \
PORT OF TACOMA
DISPOSAL SITE "D"
.. \ //t v
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w
-V';
»' • v',-'>-X
/\,/ /-¦
^ PUYALLUP RIVER/RAILROAD ^
DISPOSAL SITE / * %
/• 4
%
\
i
\ PORT OF TACOMA
6 ~ DISPOSAL SITE "E"
DISPOSAL SITE
- HYLEBOS CREEK
< DISPOSAL SITE #2
1 MILE
SCALE 1:24000
i
1000 FEET 0
1000 2000 3000
FIGURE 3-13: POTENTIAL UPLAND DISPOSAL SITES
IN COMMENCEMENT BAY, WASHINGTOH
3~30/' V ' " *
\ \v^
-------
has been identified as a wetland pasture; the remainder is under agricultural
cultivation. Ownership is by the UPRR, although the former, meandering river
channel through the site is claimed by the Puyallup Tribe. The site is zoned
M-2 (Light Manufacturing) by the city of Fife. Water from the site would be
discharged into the Puyallup River.
(2) Limitations. The site has very large capacity, even without
filling to +35 feet MLLW. Fill would also eliminate approximately 25 acres of
freshwater wetlands.
(3) Information Needs. Little is known about this site. Detailed
hydrological, geotechnical, and environmental investigations would be
necessary. Availability of the site is also unknown.
d. Port of Tacoma Site "E".
(1) Description. This site is located southeast of the head of Blair
Waterway and adjacent to the Tacoma Throughway. It is bounded by Word Road to
the south and Franck Road to the east. The site is within 1 mile from Blair
and Hylebos Waterways and has been used for dredged material disposal in the
recent past. Current elevation of the 71-acre site is +20 feet MLLW. Capa-
city for fill to +35 feet MLLW is 1.7 million c.y. The site is owned by the
Port of Tacoma and zoned S-10 (Port Industrial) by the city of Tacoma. At the
present time, the port has no tenant or plans to develop the site. The dis-
charge path for this site would be through the existing drainage channel and
creek and into the lower end of the Hylebos Waterway.
(2) Limitations. Filling the site would raise it above normal
industrial level and reduce its land use value. As the site is only sparsely
vegetated, its environmental value is judged to be relatively low.
(3) Information Needs. Same as Port of Tacoma Site "D".
e. Hylebos Creek Sites Nos. 1 and 2.
(1) Description. These two sites are located east of 54th Avenue
East on the north and south sides of 8th Street. Both sites lie within 1 mile
of the head of Blair and Hylebos Waterways. Both sites are at approximately
+9 feet MLLW; site No. 1, to the north of 8th Street, is 25 acres and site
No. 2, to the south, is 20 acres. Filled to +20 feet MLLW, capacity of site
No. 1 is 450,000 c.y. and site No. 2 is 325,000 c.y. for a total capacity of
775,000 c.y. Filling both sites to +35 feet MLLW would generate an additional
1 million c.y. capacity. The two sites are under multiple ownership and have
been zoned A-l (Manufacturing) by Pierce County. The two sites are presently
being cultivated for agriculture. The discharge path from these sites would
be either into the small creek that runs between the sites and the hill to the
west or via a new channel that connects with the existing drainage channel for
disposal site ME".
3-31
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(2) Limitations. The two sites provide an ideal opportunity to use a
two-cell disposal and treatment system. Dredged material could be hydrau-
lically deposited into the first cell and the return effluent treated in the
second cell. Hylebos Creek is located adjacent to the northern site and could
receive the treated effluent. Use of the two sites would substantially alter
existing land use. Availability is unknown.
(3) Information Needs. Similar to the Puyallup River/Railroad site.
3.05.04 Nearshore Sites. Nearshore sites are all located along or within
Taconta Harbor waterways. This report considers six nearshore sites located in
Commencement Bay (figure 3-14). A brief description of each site is provided
that includes a limited evaluation of the site's strengths and weaknesses.
Material placed in these disposal sites will eventually form two distinct
layers. Fill placed below the higher tide elevations will remain saturated at
all times due to ground water, marine water intrusion, and precipitation,
whereas the material above this elevation will drain and become seasonally or
permanently dry. Thus, nearshore disposal offers some option in placing
material that should remain saturated or unsaturated. Capacities for these
sites are expressed as two figures: the first figure provides capacity of the
site from its existing elevation to the approximate mean high tide elevation
in Commencement Bay (+12 feet MLLW); the second figure indicates capacity of
the site between +12 and +18 feet MLLW. At least 2 feet of cap was assumed to
bring the sites to industrial elevation.
Generic problems with nearshore disposal have been discussed earlier in this
chapter. Environmental effects (particularly to salmonid resources) are
potentially severe and normally require mitigation.
Testing of existing shoaled material may be necessary to assure that no
hazardous waste is buried. Treatment and monitoring could be difficult and
perhaps impossible for some contaminants. Discharge pathways for all sites
would be into the adjacent waterway.
a. Middle Waterway Site.
(1) Description. Middle Waterway is located between City Waterway to
the south and St. Paul Waterway to the north. The waterway has shoaled into
the intertidal range at its inner end and is quite shallow throughout with an
average elevation of -7 feet MLLW; although medium draft tugboats are still
able to utilize the outer third of the waterway. The 27-acre site has a total
capacity of 650,000 c.y., of which 390,000 c.y. would be "wet" (below +12 feet
MLLW) and 260,000 c.y. would be "dry." Users and adjacent landowners include
Foss Towing, UPRR, St. Regis Paper Company, Paxport Mills, and others. Foss
has indicated a desire to stay or to maintain its moorage at the outer end of
the waterway. Paxport Mills, under recent Federal permit action, has placed a
small fill along the waterway; mitigation of a resulting wetland loss was a
condition of the permit. Ownership of the waterway is with the State of
Washington.
3-32
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^Course
Light
HYLEBOS
DISPOSAL SITE #1
OUTER
Grain
Elevators,
> /. HYLEBOS
>£'¦*DISPOSAL SITE #2
MILWAUKEE WATERWAYj
DISPOSAL SITE *
*1 /i
I) S». /?> ,.SJ> „\
BLAIR GRAVING DOCK
DISPOSAL SITE
MIDDLE WATERWAY
DISPOSAL SITE
BOUNDARY'
CITY
'FIFE
SCALE 1:24000
1 MILE
1000 FEET 0
FIGURE 3-14: POTENTIAL NEARSHORE DISPOSAL SITES
IN COMMENCEMENT BAY, WASHINGTON
i;;-V iil
-------
(2) Limitations. Although the waterway is somewhat in decline, it is
still a working waterway. Filling would adversely affect those businesses and
industries along the waterway that still rely on water transportation for part
or all of their operation. The site would be able to accept materials dredged
by any method.
(3) Information Needs. A variety of environmental information will
be necessary to determine adverse effects. Detailed geotechnical and
hydrology information will be needed to design containment dikes.
b. Milwaukee Waterway Site.
(1) Description. Milwaukee Waterway is located between the Puyallup
River to the south and Sitcum Waterway to the north. Average site elevation
is -26 feet MLLW and the waterway covers approximately 30 acres. Wet capacity
is estimated at 1,870,000 c.y.; dry capacity is 290,000 c.y.; total is
2,160,000 c.y. The site has been recently acquired by the Port of Tacoma who
has filed a permit application (PN 071-OYB-2-006175) to fill the waterway to
accomodate Sea-Land's operations and to develop a container terminal facil-
ity. Although the waterway has been used by deep-draft navigation in the
past, such use in recent years has been infrequent. The waterway is also the
primary disposal site for the Corps of Engineers' proposed navigation improve-
ments project for Blair and Sitcum Waterways. The site is zoned S-10 (Port
Industrial) by the city of Tacoma. Contaminated materials are suspected to
exist within the waterway.
(2) Limitations. The port would prefer to develop this site in the
near future (2 years) rather than wait for Superfund results or for authoriza-
tion of the Corps of Engineers' navigation improvements project. Otherwise,
limitations are virtually identical to Middle Waterway; although there are
currently fewer users of Milwaukee Waterway as a navigation waterway.
(3) Information Needs. Environmental descriptions and impacts
information is being developed for a Federal environmental impact statement to
evaluate the port's permit application.
c. Blair Waterway Slips.
(1) Description. The three slips are located on the south side of
Blair Waterway at the outer end. The outer and middle slips are used for
deep-draft navigation; the inner slip is presently used for shallow draft
moorage by commercial fishing vessels. The outer slip is owned by the State
of Washington and the middle and inner slips are owned by the Port of Tacoma.
The area is zoned S-10 (Port Industrial) by the City of Tacoma.
Average elevation of the 7-acre outer slip is -30 feet MLLW. The slip lies
bayward of Pier No. 1 and would have to be diked along Commencement Bay.
Total capacity is 892,000 c.y., 825,000 c.y. wet and 67,000 c.y. dry.
3-34
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The 8-acre middle slip lies between Piers No. 1 and 2 and has an average
elevation of -30 feet MLLW. Total capacity is 945,000 c.y., 868,000 c.y, wet
and 77,000 c.y. dry.
The inner slip is 12 acres and has an average elevation of -13 feet MLLW.
Total capacity for the slip is 600,000 c.y., 484,000 c.y. wet and 116,000 c.y.
dry.
(2) Limitations. The Port of Tacoma plans to fill these slips in the
long term; however, at present they have no immediate need to fill the outer
or middle slips. The port would like to fill the inner slip and had an
approved Federal permit (issued in 1974, but currently expired) for this
action. A condition of the permit required relocating the fishing fleet and
the port was unable to meet this condition. The port has indicated that they
would prefer to see any filling completed in a relatively short time frame to
maximize the industrial use of the site. The multiple sites provide for large
capacity and allow a multiple cell system for effluent treatment. The area is
heavily industrial, however, and lengthy filling could disrupt ongoing uses.
The outer and middle slips would require dikes approximately 48 feet high.
Construction of such structures would probably require staged construction
over at least 2 years. Filling of the inner slip would displace the existing
fishing fleet.
(3) Information Needs. Similar to Middle Waterway site.
d. Blair Graving Dock.
(1) Description. The site is located on the north side of Blair
Waterway approximately 1,000 feet east of Lincoln Avenue. The site was
excavated to -5 feet MLLW and used to construct the pontoons for the rebuilt
Hood Canal Floating Bridge. The 700-foot by 500-foot rectangular site has a
200-foot-long opening onto Blair Waterway. Total capacity is 200,000 c.y.,
136,000 c.y. wet and 64,000 c.y. dry. The site is owned by the Port of Tacoma
and is currently under lease to the J.A. Jones Company; the lease expires in
January 1986, at which time the port has the option of requiring the leasee to
refill the site or to leave it as is. Zoning is S-10 (Port Industrial) by the
city of Tacoma.
(2) Limitations. Filling of this site would displace the graving
dock function from the bay.
(3) Information Needs. Geotechnical and hydrologic information is
needed. It is unlikely that extensive environmental studies will be necessary.
e. Hylebos Waterway No. 1.
(1) Description. The site is located on the north side of Hylebos
Waterway, immediately west of the East 11th Street Bridge, and is bordered to
the north by Marine View Drive. Average elevation over the 74-acre area is
-10 feet MLLW; however, the site is a combination of subtidal and intertidal
3-35
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habitats containing the last tidal marsh in Commencement Bay. The site was
the subject of a previous Federal permit application (PN 071-OYB-1-001200)
that was withdrawn in 1978. Total capacity is calculated at 1 ,274 ,000 c.y. ,
of which 550,000 c.y. would be wet and 724,000 c.y. would be dry. The site is
owned by the Port of Tacoma and is zoned S-ll (Industrial) by the city of
Tacoma.
(2) Limitations. Strong objections to filling of this wetland are
expected from the Puyallup Tribe and environmental agencies and interest
groups. Mitigation for the loss would be difficult.
(3) Information Needs. Similar to Middle Waterway. Environmental
investigations on splmonid use and importance could be extensive.
f. Hylebos Waterway No. 2.
(1) Description. This site is located in the same approximate area
as Hylebos Waterway No. 1 but is east of the bridge and inside the waterway.
The site is bordered by Marine View Drive to the north and the Sound Refining
Company to the east. Like Hylebos Waterway No. 1, the area is a combination
of subtidal and intertidal, sloping northward from the waterway to high ground
along Marine View Drive, and is presently being used for log storage. Capa-
city of the 24-acre site totals 300,000 c.y., approximately 70,000 c.y. wet
and 230,000 c.y. dry. The site is owned by the Sound Refining Company, which
has held meetings in anticipation of filing for necessary permits to fill the
site for plant expansion. The site is zoned S-ll (industrial) by the city of
Tacoma.
(2) Limitations. Same as Hylebos Waterway No. 1.
(3) Information Needs. Same as Hylebos Waterway No. 1.
3.05.05 Off-site Options. Off-site disposal would involve use of one of the
three disposal methods(open water, upland, or nearshore) at sites located
outside of the Commencement Bay area. The differences between local and
off-site disposal involve increased costs for transportation of the contami-
nated materials to the off-site disposal area and the problems of retaining
the contaminants during that transport. The latter problem can be effectively
handled by current technologies associated with transportation of hazardous
materials; it is, however, expensive. The most common forms of long distance
transport of dredged material would be barges, trucks, and railcars. All of
these carriers could be made watertight or the material dewatered and then
loaded. The potential for release of contaminants is increased, however, by
this rehandling. The increased costs would depend upon the transportation
mode selected and associated controls and treatments required. Barging of
dredged material to an open-water site outside of the Commencement Bay area
was considered initially, but was dropped because no likely specific site
could be identified based on existing information.
3-36
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Off-site disposal would seem to be justified only if at least one of the
following criteria were met:
o No local disposal options were available that could accommodate either
the volume or degree of contamination of sediments dredged.
o A regional disposal site and protocol existed for contaminated sediment.
o The material contained contaminant fractions that require treatment
that is not available locally.
o Local public and/or political pressures rendered local disposal of
contaminated sediments impossible.
3-3?
-------
CHAPTER 4.0 SITE CONTROL AND TREATMENT PRACTICES
4.01 Introduction. Conventional site control and treatment measures are
typically applied to and designed for a specific disposal site after dredging
and disposal methods have been selected. The purpose of these measures is to
ensure that material loss from a disposal site meets applicable environmental
criteria. For contaminated materials, site control and treatment requirements
can represent a controlling cost factor that must be considered prior to
selection of the dredge and disposal site for a given job.
Site control measures addressed in this chapter all pertain to contaminant
confinement within a selected area and isolation from the environment during
and after disposal of contaminated sediments. Treatment practices include
those physical» chemical, or biological processes that can be applied to con-
taminants in either the sediment-bound (solids), soluble, or gaseous phase
resulting from the disposal of contaminated dredged material in open-water,
nearshore, or upland disposal sites. In addition to site control and treat-
ment, discussions are presented on biological control of disposal areas and
appropriate monitoring requirements for each disposal method, as well as
remedial response to monitoring indications. A summary of the site control
and treatment alternatives is presented in chapter 6 in order of increasing
degree or level of total contaminant removal. This hierarchical approach
allows the decisionmaker to view varying levels of control with respect to
overall degree of protection afforded and effects of increasing degrees of
protection on costs.
4.02 Site Controls for Disposal.
4.02.01 Overview. Potential impacts resulting from loss of contaminants
during and after dredging and disposal operations may require that certain
physical or chemical controls be used for open-water, nearshore, and upland
disposal sites. Controls are containment techniques, and typically include
lining with soil or synthetic membranes, capping, or cover and run on control
operations; physical and chemical stabilization of contaminated materials to
minimize escape of contaminants; and collection, dewatering, and treatment of
effluent, runoff, and leachate. Not all of the measures apply to each dis-
posal site; however, common practices include capping and lining operations.
Since many control and treatment measures are similar for nearshore and upland
disposal sites, these disposal alternatives will be discussed together below.
4.02.02 Controls for Open-Water Disposal. Feasible options available for
implementing open-water disposal with controls include submerging the dis-
charge (submerged diffuser shown in figure 3-2), confining the dredged mate-
rial subaqueously (submerged dikes shown in figures 3-5 and 3-6), and capping
the dredged material subaqueously (figure 4-1). All of these controls can be
considered to be a part of the capping control option. Placement of contami-
nated sediments and cap materials is discussed in chapter 3. Types of capping
materials and stability of the cap are discussed below.
4-1
-------
DISCHARGE
LINE
DERRICK
WATER SURFACE
SUBMERGED DIFFUSER
(CLEAN SAND, ETC.)
w ,
CAPPING MATERIAL
CONTAMINATED DREDGED MATERIAL
BOTTOM SEDIMENT
Figure 4-1: Capping With Submerged Diffuser
-------
a. Capping Materials. There has been a significant amount of research
devoted to cover materials for burial of hazardous spills in lakes and water-
ways. This research, summarized by Hand, et al. (1978), also applies to cap-
ping contaminated dredged material. Materials, both naturally occurring and
manmade, that can be used to cover contaminated dredged material are divided
into three categories: inert, chemically active, and sealing agents. Of
these, only inert materials are likely to be successfully used in Commencetnent
Bay.
Inert materials include coarse- and fine-grained soils. Research is being
performed at the WES to determine covering depths required to inhibit bio-
turbation of the contaminated materials and to retard leaching of contaminants
into the water column. When soils are used as capping materials they should
be thick enough to protect the underlying deposit from disturbances caused by
storm generated waves, propeller wash from navigation traffic, and to bury the
contaminated sediments out of the reach of benthic organisms. The nature of
the capping material will influence the depth and character of burrowing.
Myers (1979) reported that a sand cap will attract suspension feeding organisms
that should not be expected to be deep burrowers, while deep burrowing deposit
feeders will colonize a fine-grained cap. Therefore, site-specific biological
populations (such as the deep-burrowing geoduck clam) are important in
designing the cap thickness. Bokunieweiz (1981) reported that for disposal
sites in relatively protected, nearshore waters, a cap thickness of less than
a meter should be sufficient, but site-specific studies should be done to
evaluate biological populations and erosion potential.
Capping with chemically active materials involves the placement of a chemical
compound over the contaminated dredged material that would react with the
contaminants to neutralize or otherwise decrease toxicity. This strategy
differs from the use of inert materials in that each contaminated dredged
material must be dealt with on a case-by-case basis. Carbon compounds are a
common example of chemically active ingredients that can be added to a cap.
In the capping of dredged material, the active material should be combined
with an inert stabilizer to provide stability to the cap. Another approach
would be to cover the active covering layer with an erosion-resistant inert
layer. The inert layer would also provide protection for the benthic
organisms. While the inert covers have little or no chemically related impact
on the organisms, the chemically active covering agents could be harmful to
some organisms. Also, greater accuracy would be required for placement of the
chemically active materials.
Sealing agents include grout, cements, and polymer films. The unique feature
of the grouts and cements is that, when placed on top of contaminanted sedi-
ments, they will harden and form a crust, preventing erosion and resuspension
of the contaminated material. A Japanese firm (Takenaka Komuten, 1976) has
done work in dredged material stabilization and deep mixing of sediments using
grouting compounds. Also(grouting is often used in the offshore oil industry
for stabilization of oil producing facilities. The technology for using grout
in the saltwater environment is well developed and it could be adapted for use
in capping contaminated dredged material. However, there are some disadvan-
tages associated with the use of grout in capping dredged material. The thin
4-3
-------
layer of grout placed over the contaminated material cannot be considered as a
permanent cap material. It should be used with a covering of inert material
to provide additional stability and habitat for benthic organisms. There
could also be problems with the grout cracking as the contaminated dredged
material consolidates with time.
Polymer film systems have been the subject of a report by Widman and Epstein
(1972). They proposed barge mounted deployment systems for either hot or cold
application of polymer film overlays. The application systems included those
for placing coagulable polymers , hot melt materials, and preformed commer-
cially available films. The application system for the preformed overlay
limited its application to water depths of 25 to 30 feet. Roe, et al. (1970),
reported on a chemical overlay system which included 2,000-square feet per
hour coverage and availability for water depths up to 120 feet. Concepts for
the use of polymer film overlays for cover of contaminated dredged material
were developed from early erosion control efforts related to marine salvage
work. None of the concepts have been field tested for dredged material. The
major limitation to these concepts involves the design, construction, and cost
of capital equipment required to place them.
Capping is currently being carried out in the Long Island Sound and New York
Bight as a means of controlling the potential harm of contaminated or other-
wise unacceptable sediments. All of these capping projects have used inert
natural materials for covering the contaminated sediments. A significant
amount of research has been performed on stability and biological activity of
inert cap materials (Bokuniewiez, et al., 1981; Freeland, et al., 1983;
Morton, 1983; O'Conner, 1983; Brannon, et al., 1983). Based on these past
experiences, capping using only inert materials in Commencement Bay is con-
sidered to be a feasible treatment alternative for some of the contaminated
sediments. Costs for inert capping are discussed in chapter 5.
b. Stability of Capping Materials. Stability of the capping material is
a major concern in the design of capping projects. Factors influencing cap
erosion include: (1) the particles (size, uniformity, shape, size distribu-
tion, texture, etc.); (2) the hydrodynamics of the system; (3) slope of the
mound; and (4) the degree of cap material cohesiveness. Therefore, the
prediction of erosion potential of a capping material should be made on the
basis of site specific data. The inert materials used for capping can be
classified as cohesive or noncohesive. For given erosive forces, movement of
noncohesive particles depends on shape, size, and density of discrete parti-
cles and on the relative position of the particle with respect to surrounding
particles. The movement of cohesive particles depends on those factors cited
above for noncohesive particles as well as on the strength of the cohesive
bond between particles. This latter resisting force can be much more impor-
tant than the influence of the characteristics of the individual particles.
Cohesive capping materials excavated by mechanical dredges will be more
resistant to erosion than those excavated by hydraulic dredges. Once the
cohesive bond has been broken during the hydraulic dredging process, the
individual particles and floes behave essentially as noncohesive particles
until they gain strength through the consolidation process. The degree of
4-4
-------
consolidation, which is inversely proportional to the interstitial water
content, has a significant effect on the ease at which the fine-grained
particles will erode. The time required for the complete consolidation of
fine-grained capping material will be many years if the material is pre-
dominantly clay.
A problem with capping in underwater sites is the difficulty of assessing the
dispersion of the contaminated mass to be covered by the cap. Contaminated
materials placed in an open-water site without the use of an underwater
diffuser may be spread over a wide area by stratification of the water column
from thermoclines or currents, or by bottom currents. Fine particles, to
which most of the bound contaminants are attached, are the most likely to be
distributed over a wide area. Postdisposal sampling of the area for contami-
nant distribution would probably be necessary for level bottom open-water
disposal.
Another problem with underwater capping is the potential for displacement of
the contaminated mass by capping. Depending upon substrate firmness and the
density of the contaminated mass, the cap material may displace and redistri-
bute the contaminated materials, especially if the capping material is of a
higher density or coarser size than the contaminated material. Determination
of the potential for mass failure and dispersion would require testing with
materials physically similar to those which will be placed underwater.
4.02.03 Controls for Upland and Nearshore Disposal.
a. Background. Diked upland and nearshore containment areas are used to
retain dredged material solids while allowing the carrier water or entrained
water to be released from the containment area. This section discusses appro-
priate controls that can be applied to the containment of contaminants in
nearshore and upland disposal sites.
b. Liners. A variety of liner materials are available for use in con-
fined disposal operations. Principal characteristics, advantages, and dis-
advantages of liners and flexible membranes are listed in table 4-1. Soil
liners are expected to be the only liner necessary for most disposal of
dredged material at upland and nearshore sites. However, in certain upland
applications, a combination of synthetic membrane and soil liner may be
required to achieve maximum containment of contaminants. To ensure continued
effectiveness of the liners, whether soil or flexible membrane, they must be
compatible with the dredged material and leachate they are to contain and be
properly installed.
(1) Soil Liners. Soil liners are generally adequate for most dredged
material disposal sites and are recommended for use on the sides and bottom of
upland areas containing contaminated material. In general, clay is a good
liner material that is not only relatively inert to chemical attack but will
also act as a filter, absorbing many contaminants from the leachate (Kelley,
1982). Unfortunately, the chemical compatibility of clay soils with leachate
4-5
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liner material
Characteristics
Range of
costs1
Advantages
Disadvantages
Soils:
Compacted clay
sons
Soilbentonite
Compacted mixture of onsite soils
to a permeability of tO~7cm/sec
Compacted mixture of onsite soil,
water and bentonlie
4dmlx»$:
Asphalt-concrete Mixtures of asphalt cement and
high quality mineral aggregate
Asphatt- Core layer of blown asphalt
membrane blended wiih mineral fillers and
reinforcing fibers
Soil asphalt Compacted mixture of asphalt,
water, and selected ln-place
SOilS
Soil cement Compacted mixture of Portland
cement, water, and selected in-
place soils
Polymtrtc m$mbrtn$s:
Butyl rubber Copolymer of Isobuiylene wiih
small amounts of Isoprene
Chlorinated
polyethylene
Ch'orosulfonaie
polyethylene
Elasticued
polyolelins
Epichiorohydrin
rubbers
Ethylene
propylene
rubber
Neoprene
Polyethylene
Polyvinyl
Chlorldo
Thermoplastic
elastomers
Produced by chemical reaction
between chlorine and high
density polyethylene
family of polmers prepared by
reacting polyethylene with
chlorine and sulfur dioxide
Blend ol rubbery and crystalline
polyoleflns
Saturated high molecular weight,
aliphatic poieihers with chloro-
methyl side chains
Family of terpoiymers of ethylene,
propylene, and nonconjugated
hydrocarbon
Synthetic rubber based on
chloroprene
Thermoplastic polymer based on
ethylene
Produced In roll form In various
wfdths and thicknesses; poly*
meruation of vinyl thtonde
monomer
Relatively new class of polymeric
materials ringing from highly
polar to nonpo'ar
High cation exchange capacity;
resistant 10 many types of
leachaie
High cation exchange capacity;
resistant to many types of
leachate
Resistant to water and effects of
weather extremes; stable on
side slopes; resistant to acids,
bases, and inorganic salts
Flexible enough to conform to
irregularities in subgrade; resist*
ant to acids, bases, and
inorganic salts
Resistant to acids, bases, and
salts
Organic or inorganic acids 0'
bases may soiubilije portions ol
day structure
Organic or inorganic acids or
bases may soiubilize portons of
clay structure
Not resistant to organic solvents;
partially or wholly soluble in
hydrocarbons; does not have
good resistance to inorganic
chemicals; high gas
permeability
Ages rapidly in hot climates; not
resistant to organic solvents,
particularly hydrocarbons
Not resistant to organic solvents,
particularly hydrocarbons
Good weathering (n wet-dry/freeie- Degraded by highly acidic
thaw cycles; can resist moder- environments
ale amount of alkali, organics
and inorganic salts
Low gas and waler vapor perme-
ability. thermal lability; only
sltghily allecltd by oxygenated
solvents and other polar liquids
Good tensile strength and elonga-
tion strength; resistant to many
inorganics
Good resistance to o-jone, heal,
acids, and alkalis
low density; highly resistant to
weathering, alkalis, and acids
Good tensile and leat strength;
therm.il stability; low rate of gas
and vapor permeability; resist-
ant to ozone and weathering;
resistant to hydrocarbons, sol-
vents, fuels, and oils
Resistant to dilute concentrations
of acids, alkalis, silicates, phos-
phates and brine; tolerates
extrerr.e temperatures; flexible
at low temperatures; excellent
resistance to weather and ultra-
violel exposure
Resistant to oils, weathering,
ozone and ultraviolet radiation;
resislant to puncture, abrasion,
and mechanical damage
Superior resistance to oils,
solvents, and permeation by
water vapor and gases
Good resistance to Inorganics;
good tensile, elongation,
punttuie, and abrasion leststanl
properties; wide ranges of
physical properties
Excellent oil, fuel, and water
resist-
ance with hign tensile strength
and excellent resistance to
weathering and ojone
Highly swollen by hydtoca*bon
solvents and pe'.roieum oils;
difficult 10 searr. a,id repair
Will swell in presence of aromatic
hydrocarbons and oils
Tends to harden on aging; 'ow
tensile strength; tenaency 10
shrink from exposure to sun-
light; poor resistance to oil
DiMicullies with low tempera'.uiet
and oils
None reported
Not recommended for petroleum
solvents or halogenated
solvents
None reported
Not recommended for exposure 10
weaihering and ultraviolet iigM
conditions
Attacked by many organics.
including hydrocarbons, sol-
vents and ©Us; not recom-
mended for exposure to weattv
ering and ultraviolet llfiht
conditions
None reported
•l. - St to W ln»iaiie9 cotit par »q yd In tost dolU't, M -
SOURCE: "Compared** evaluation «t Incinerators and UnciUli,
to 14 per tq yd.; M - U to SW per tq. yd.
' prepared tor the Cftemkal menuitctveu uioclalton, by EnQtntermg Science. McL*aA,Vfc. May 1(62.
Table 4-1: Summary of Liner Typaa
4-6
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is based on limited data and experience; particularly for dredged material.
Both organic and inorganic acids and bases may solubilize portions of the clay
structure. The results of compatibility testing of clay with different
organic and inorganic fluids have indicated the need not only for more labora-
tory testing, but also a need for fieldwork to determine validity of the
generalizations obtained from previous hazardous waste studies (Green, 1983).
Construction of soil liners to achieve remolded permeability of 1 x 10~7
cm/sec or less is recommended. The soil may be obtained onsite, from selected
borrow areas, or from off-site sources. If available soils do not have the
required low permeability, they can be blended with clay soils, bentonite, or
other additives. Prepared bentonite formulations would probably be required
for Commencement Bay sediments due to high salt content. Soil liners placed
in a minimum 3-foot-thick layer are recommended.
(2) Flexible Membrane Liners. Synthetic membrane technology is new
and a variety of synthetic materials and compounds are being manufactured,
tested, and marketed. The various membranes being produced vary not only in
physical and chemical properties but also in installation procedures, costs,
and chemical compatibility with waste fluids. The liners range in thickness
from 20 mil to 140 rail and are made from polymers of rubber, plastics such as
PVC, polyolefins, and thermoplastic elastomers.
Since the prime purpose of the liner is to prevent leachate from escaping the
disposal site, the physical integrity and chemical compatibility of the liner
with the leachate must be ensured. Potential incompatible combinations of
wastes and liners include the following:
o Polyvinyl chloride (PVC) tends to be dissolved by chlorinated
solvents.
o Chlorosulfonated polyethylene can be dissolved by aromatic
hydrocarbons.
o Asphaltic materials may dissolve in oily wastes.
o Concrete and lime based materials are dissolved by acids.
Expected life of synthetic liners is less than 30 years. In general, most
polymeric material will tend to swell when exposed to fluids. Cross linking
or vulcanizing a polymer or rubber will reduce its ability to swell in a
solvent. Swelling usually has adverse effects on a polymer material. Some of
the major effects of swelling are:
o softening,
o loss of tensile and mechanical strength and elongation,
o increased permeability and potential for creep, and
o increased susceptibility to polymer degradation.
4-7
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Synthetic membranes are also subject to biological and ultraviolet light
degradation.
(3) Limitations. Because there is currently no adequate method for
successfully placing impermeable synthetic liners underwater, lining of near-
shore sites is limited to the use of a soil liner. The material would be
placed as a high density slurry layer and allowed to settle and consolidate.
In upland sites, soil liners if allowed to dry would crack and lose inte-
grity. Soil liners are subject to differential settlement and bioturbation
prior to filling. Liner life will be highly site specific. Once exchangeable
adsorption sites are filled within the liner, soluble contaminants will slowly
migrate through the liner by diffusion.
Synthetic membrane liners are applicable only to the upland sites. They
cannot be installed in areas of tidal influence or high ground water table.
Synthetic liners are subject to leaks at field jointed seams, need physical
protection, and are not self sealing if punctured. Physical and chemical
integrity is highly site specific and dependent upon liner compatibility with
dredged material and leachate.
c. Covers and Run On Control. Surface capping or covering in upland or
nearshore sites is the placement of clean, low permeability material, usually
3 feet thick, over the confined dredged material. Surface capping is placed
over the site to:
o reduce surface water run on,
o reduce surface water infiltration,
o reduce water erosion,
o reduce wind erosion and fugitive dust emission,
o contain and control gases and odors,
o provide a surface for vegetation and other postclosure uses, and
o prevent direct bioturbation (human and animal).
Covering of the material in upland and nearshore sites will be required
intermittently (at end of each dredging cycle) and at final site closure.
Various low permeable materials may be used, including soils and clays,
admixtures (e.g., asphalt concrete, soil cement), and polymeric membranes
(e.g., rubber and plastic linings). Typical final covers are composed of
several layers. Run on control is also possible through barriers constructed
on the high-ground side of the site.
(1) Cover Types. Two examples of layered cover systems are shown in
figure 4-2 and the function of each layer is shown in table 4-2. A gravel
layer or structure to break capillary pumping of moisture from the dredged
material should be included to reduce upward migration of contaminants through
the cap and surfacing of contaminated water as runoff. This biobarrier will
also reduce cap penetration by roots of cover vegetation and by burrowing
animals.
4-8
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TABLE 4-2
PRIMARY FUNCTION OF COVER LAYERS
Lay
er
Reduce
Run On and
Infiltration
Barrier
Buffer
Filter
Gas Channel
Top Soil
Reduce
Water
Erosion
Reduce
Wind
Eros ion/
Dust
Emiss ions
Control
Gases
and
Odors
Provide
Surface
For
Vegetation
Enhance
Cover
Integrity
X
X
(2) Limitations. Some volatiles could continue to escape by diffu-
sion and convection generated by atmospheric pressure changes (barometric
pumping). Differential settlement due to consolidation of filled materials
could cause cracking and leaking of the cap.
d. Underdrain9. Leachate collection by underdrainage applies primarily
to the upland disposal sites. It is also theoretically possible to stage
disposal in a nearshore environment such that underdrains could be used to
dewater the upper layer (unsaturated zone above tide line) of nearshore
disposal sites. Underdrainage is a dewatering method which may be used either
individually or in conjunction with improved surface drainage. In this
procedure, collector pipes are placed in either a naturally occurring or
artificially placed pervious layer prior to dredged material disposal. Upon
disposal, free water in the dredged material migrates into the pervious under-
drainage layer and is removed via the collector pipe system. Two mechanisms
exist for dewatering and densification of fine-grained dredged material using
pervious underdrainage layers:
(1) Gravity Underdrainage. This technique consists of providing free
drainage at the base of the dredged material. Downward flow of water from the
dredged material into the underdrainage layer takes place by gravity.
(2) Vacuum Assisted Underdrainage. This technique is similar to
gravity underdrainage, but a partial vacuum is maintained in the underdrainage
layer by vacuum pumping.
Design of an underdrainage layer for use with dredged material is somewhat
different than design of a normal pervious filter. A continuous flow condi-
tion is usually not maintained in the underdrainage layer. Water essentially
drips from the dredged material, and the static water level in the under-
drainage layer is at the flowline of the collector pipe system. Fine-grained
dredged material placed in confined disposal areas tends to exhibit individu-
alized particle behavior, and it is necessary to choose a filter material that
will resist both filter clogging and piping of the fine-grained dredged
material through the filter.
4-9
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LOAM (FOR VEGETATION)
V0 OOP OOOOO OOOO CJTT99WI
CLAY (BARRIER)
DOOOOOOOOOOC
C.OOOOOOOOOOOOOOOC
UUUUUULUTJUOUl'PJUPOOOy
7
2
TfToboo'coo'ooooooc coo
300000&&C OOOOC'OC
oooooooooooooooo. GRAVEL (GAS CHANNEL) j888$888lt!Si!S8
ooooooooooooooooc
oooooooooooooooo
OOOOOOOOOoooooooooooooooooovOOOOoo
ooooooooooooocoooooo
OOOOOOOGGCOOOOC-GO
LOAM
^//^//y/7/ ci^ay'( barr ier)
U
SILT (FILTER)
1 i i i i ¦ 1 ¦ ¦
SAND (BUFFER)
Figure 4-2: Examples of surface Cover Systems
4-10
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When placing underdrainage material over a liner for leachate collection, two
choices are available: (1) creation of a drainage blanket and collector pipe
system covering the entire site or (2) creation of a radial or herringbone-
type underdrainage layer containing collector pipe. Which of these choices is
most appropriate and cost effective is again a site-specific design problem.
(3) Limitations. All leachate collection underdrainage systems must
be installed prior to disposal, but can be expected to last for long periods
of time. If there is large drain spacing and a leak in the liner, leachate
underdrainage may not collect all of the leachate. Drainage water (leachate)
will persist for a long time at a slow rate of production.
e. Stabilization of Sediment. Sediment stabilization is useful for both
bulk treatment and surface treatment. The stabilization of sediment in bulk
can be done only for upland and nearshore sites and not for open-water sites.
Surface stabilization may be used for all sites. Stabilization can be done
through the use of chemical and physical stabilization techniques depending on
the sediment composition. Physical techniques include the use of barriers to
lower the velocity of the wind locally or to prevent wind from contacting the
contaminated particulates. The introduction of soil surface barriers such as
a gravel layer or soil blending are also effective physical stabilization
techniques. Chemical stabilization includes the use of both mix up and spray
on (surface applied) chemical additives. These materials prevent dust
entrainment by causing the dust particles to adhere to one another, creating a
smoother surface and a large mass that cannot be easily resuspended.
(1) Lime Treated Sediment. Lime addition to sediments has many
beneficial effects. It is useful for both bulk and surface stabilization; it
may be particularly useful for treating capping materials. Lime is mixed into
clays for its effects as a flocculant. Lime will also promote some beneficial
pozzolanic or cementing reaction in fine, cohesive soils which may continue to
strengthen for many weeks. Lime addition will also raise the sediment pH and
retard heavy metal release. Lime is used in combination with other additives
such as fly ash. Although fly ash is not a cement in itself, when used in
combination with lime or cement and water, fly ash will develop cenientatious
properties. The proportioning of soil, lime, and fly ash is dictated by
economy and the desired properties in normal soil stabilization. Depending on
the scarcity of cover soil or the availability of fly ash nearby, a normal mix
for stabilization may include 20 percent fly ash, 5 percent lime, and 75 per-
cent soil. However, mixtures containing 60 percent fly ash, 5 percent lime,
and 35 percent sand may be just as effective.
(2) Dust Pallatives. The three general pallative methods commonly
used are agronomic, surface penetration, and admix.
Agronomic methods consist of operations required to establish or preserve
vegetative cover, mulch, shelter belts, and rough tillage. Vegetation cover
is often considered to be the most satisfactory form of dust pallative based
on esthetics, durability, cost, and maintenance. A well anchored mulch can
also be used to stabilize soil. The mulch can consist of vegetative material,
woven paper products, natural and synthetic netting, or a combination.
4-11
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Surface penetration methods for sediment stabilization are accomplished by
spraying the soil surface with a material and allowing this material to
penetrate the soil under its own accord. Depending on the material, surface
penetration applications may be accomplished with a liquid pressure distri-
butor, by a gravity flow water distributor, or by hand spraying. There are a
variety of spray on materials that can stabilize a sediment. These materials
include asphalt, concrete, soil cement, soil asphalt, catalytically blown
asphalt, and asphalt emulsions. Many of these materials can be sprayed
directly on prepared surfaces in a liquid form which then solidifies to form a
continuous membrane. Hydraulic asphalt concrete (HAC) is a hot mixture of
asphalt cement and mineral aggregate that is resistant to the growth of plants
and weather extremes and will resist slip and creep when applied to side
slopes. The material should be compacted to less than 4 percent voids to
obtain the lowest permeability possible. Soil asphalt is similar to soil
cement; however, the soil used should be a low plasticity, gravelly soil with
10 to 25 percent silty fines. Catalytically blown asphalt is manufactured
from asphalts with high softening points by blowing air through the molten
asphalt in the presence of a catalyst such as phosphorus pentoxide or ferric
chloride. The material can then be sprayed on a prepared surface regardless
of cold or wet weather. As with soil asphalt, the membrane must be water-
proofed with a hydrocarbon or bituminous seal. Asphalt emulsions can also be
sprayed directly on prepared surfaces at temperatures above freezing. These
membranes are less tough and have lower softening points than hot airblown
asphalt. However, the toughness and dimensional stability can be increased by
spraying onto supporting fabrics.
Admix methods of sediment stabilization result from blending a material with
the sediment to produce a uniform mixture. This method requires more time,
effort, and equipment than spray on techniques; however, it usually lasts
longer. A variety of materials are suitable for use in the admix operations.
The resulting soil cement is a low strength portland cement concrete with a
permeability dependent upon the type of soil used. As expected, more granular
soils produce more permeable soil cement; however, permeability coefficients
as low as 1 x 10cm/sec have resulted from the use of fine-grained soil.
Coatings such as epoxy asphalt and epoxy coal tar have been used to decrease
the permeability. Any nonorganic, well graded soil with less than 50 percent
silt and clay can be used in soil cement. The soil should have a maximum size
of 0.75 inch and a maximum clay content of 35 percent. The optimum moisture
content is that which results in a maximum density (Shafer, 1984). Other
admix soil stabilizers include chemical dispersants and swell reducers.
Soluble salts such as sodium chloride, tetrasodium pyrophosphate, and sodium
polyphosphate are added primarily to fine-grained soils with clay minerals to
deflocculate the soils, increase their density, reduce permeability, and
facilitate compaction. Additives are more effective with montmorillonite clay
than with kaolinite or illite. Bentonite is a natural clay, composed pri-
marily of montmorillonite, which is extremely fine grained and absorbent. Its
high swelling properties make it suitable for mixing with soil and water to
produce a low permeability cover layer. Any clay cover layer must be kept
moist to avoid cracking. This is usually accomplished by covering with
another soil layer in which vegetation is planted (JRB Assoc., 1982).
4-12
-------
(3) Water Sprinkling. Sprinkling the surface with water will also
limit windblown dust. The sprinkle rate must be closely matched with the
variable evaporation rate for the most efficient operation and to minimize
additional runoff.
(4) Limitations. Lime distribution from surface application does not
ensure lime contact with the entire dewatered sediment. Also a disadvantage
resulting from lime based stabilization is that the solid mass is porous. As
such, consideration should be given to sealing the surface to prevent leaching
of contained waste. Surface penetrant methods such as sprayed on asphalt have
the disadvantages of high equipment and energy costs. Also, sprayed on
asphalts have not been successful with some organic waste. Admixed methods
for stabilization such as soil cement are incompatible with some wastes such
as sodium salts of arsenate, borate, phosphate, iodate, and sulfide. Salts of
magnesium, tin, zinc, copper, and lead along with organic matter are also
incompatible. Cement is a porous solid and, therefore, contaminants can be
expected to leach out over time. Water sprinkling can be effective in the
short term but requires careful monitoring of application rates to avoid
creating additional site runoff.
f. Biological Decontamination. Seeding a waste material with micro-
organisms to achieve degradation may be feasible if the waste has been deter-
mined to be biodegradable. Biodegradation has been used most widely for
treatment of oily sludges and refinery wastes. Bacteria developed for
biological seeding are capable of degrading benzenes, phenols, cresols,
naphtolenes, gasolines, kerosenes, and cyanides (Ehrenfeld and Bass, 1983).
The biodegradation process is relatively slow. Complete degradation of the
waste could take several years and may never be complete if refractory com-
pounds such as polynuclear aromatics are present. Biodegradation is an
aerobic process for petroleum sludges and probably other organic wastes.
Therefore, this technique is generally limited to those situations where the
sediment is naturally aerated or where artificial aeration is feasible. Also,
nutrient addition (nitrogen and phosphorus) and pH adjustment (lime addition)
may be required. Thus, problems with respect to application and mixing of
nutrients and lime into the sediment will exist. In addition, the biological
decontamination treatment process is new and extensive field trials would have
to be performed.
4.03 Treatment for Nearshore and Upland Disposal Sites.
4.03.01 Introduction. There are a variety of physical, chemical, and
biological processes that have been developed for municipal and industrial
water and waste treatment requirements. Many of these processes have
potential in treating contaminated dredged material discharged at confined
nearshore and upland disposal sites. However, few processes have actually
been required for or applied to dredged material disposal. Among the
processes widely applied in confined disposal are plain sedimentation for
solids and sediment-bound contaminant removal, and chemical clarification and
filtration for enhanced removal of particulate (suspended solids), sorbed
metals, and organics. Use of activated carbon for removal of soluble organics
has received some limited application to dredged material. Other processes
4-13
-------
not previously applied to dredged material include organics oxidation, dis-
solved solids removal methods (e.g., distillation), and volatiles stripping.
This section describes and discusses each process in terms of demonstrated or
potential removal efficiencies for solids, sediment-bound contaminants,
soluble organics and metals, dissolved salts, and volatiles.
The water discharged from a disposal site will vary in quantity and quality
over time. Site effluent will be produced in large quantities for hydrau-
lically dredged sediments during the dredging process. This effluent will
usually be of lower contaminant concentration than that found in the inter-
stitial water and will almost always be of lower contaminant concentration
than that of future water discharges from the site. Runoff water will be
produced during site dewatering and periods of precipitation on the site.
Runoff will be of concern primarily during the dewatering and prior to place-
ment of a surface cap on the site. Runoff water may be of higher contaminant
concentration than the original site effluent. Leachate water is produced as
water moves through the sediments and out the sides and bottom of a disposal
site. This water is produced in the smallest quantities but may contain
relatively high contaminant concentrations and may persist for a long period
of time. Leachate treatment usually requires collection via drains placed
under the site (underdrains). This section applies mainly to treatment of
site effluent; long-term site runoff and leachate are discussed in section
4.04.
Table 4-3 lists water treatment methods and indicates which of these have been
applied to dredged material disposal. These treatment processes can be
grouped into various levels of treatment, depending upon a particular phase or
class of contaminant being removed. Four levels of treatment were identified
and are defined as follows:
0 Level I is the removal of solids and particulate-bound contaminants.
o Level II is additional treatment to remove soluble metals.
o Level III is further processing to remove soluble organics.
o Level IV is the purification of water by dissolved solids removal.
The relationships between levels of treatment are illustrated in plate 3. A
comparison of the relative efficiencies of the treatment levels is given in
table 4-4. Increasing levels of treatment result in increasing percentages of
contaminant removal. The qualitative ranges of soluble concentrations remain-
ing after each treatment level and percent removals are based on actual moni-
toring of disposal sites for Levels I and II (where applicable) and on best
available water treatment technology for Levels III and IV. It should be
noted that the estimates made for soluble organics and soluble metals removals
past Level I are mean values and represent a grouping of contaminants with
large ranges of solubility and treatability. The data in table 4-4 should be
viewed as preliminary for planning purposes only, and as such, are presented
to illustrate potential levels of removals. Actual removal efficiency data on
Commencement Bay sediments would have to be obtained through site-specific
testing, evaluations, and demonstrations.
4-14
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TABLE 4-3
LISTING OF WATER TREATMENT PROCESSES
Applied to Not Applied
Proven Proven Not Dredged to Dredged
Treatment Process Method Demonstrated Material Material
Suspended Solids
Plain Sedimentation X X
Chemical Clarification X X
Filtration X X
Soluble Metals
Precipitation X Xa
Soluble Organics
Adsorption X X
Ozonation X X
Dissolved Solids
Distillation X X
Reverse Osmosis XX X
Electrodialysis X X
Ion Exchange X X
Volatiles
Stripping X X
Leachateb
Biological X X
Physical/Chemical X^ X
a Limited success on pilot scale.
b Potential for use of existing municipal or industrial process for
treatment offsite.
4-15
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TABLE 4-4
CONTAMINANT REMOVAL EFFICIENCY OF WATER TREATMENT LEVELS!•/
Leve 1
Class of
Contaminan t
Percent
Removal
Water
Concentration Remaining
I
Solids
Me ta Is
Organics
i
80
50
39.9+
to 99+
to 90+
mg/1
ppb
ppb
range
to ppm ranged
to ppm ranged./
II
Me t a 1 s
Organics
50
99+
to 90
ppb
ppb
ranged
to ppm range^/
III
Metals
Organics
99+
95+
ppb
ppb
ranged./
range!./
IV
Metals
Organics
99+
99+
highest quality attainable!/
highest quality attainable!./
_1/Assumes influent strength defined by dredged sediments that are not
classifiable as "exti*emely hazardous waste" under RCRA (i.e., "low saturation"
influents, see last paragraph of section 6.05).
^/Concentrations based on Hoeppel, et al., 1978, and Palermo, in preparation.
3/Concentrations based on capability of "best available treatment"
technology.
4-16
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4.03.02 Plain Sedimentation.
a. Overview. Many of the contaminants present in the flow from a
hydraulic dredging operation will be removed during the plain sedimentation
occurring within a confined disposal area. Confined disposal areas are used
to retain dredged material solids while allowing the carrier water to be
released from the disposal area. The effluent may contain levels of both
dissolved and particulate-associated contaminants.
Release of supernatant waters from confined disposal sites occurs after a
retention time of up to several days. Actual withdrawal of the supernatant is
governed by the hydraulic characteristics of the ponded area and discharge
weir discussed in chapter 3 above. Procedures have been developed to predict
concentrations of suspended solids in disposal area effluents, taking into
account settling behavior of the sediment in question. All solids cannot be
retained during the disposal process, and associated contaminants are trans-
ported with particulates in the effluent to the receiving water. Therefore,
predictions of suspended solids concentrations expected in the effluent can
often be used to estimate contaminant losses and determine need for further
solids removal treatment. Similar testing can be done to determine treatment
requirements for soluble contaminants (Palermo, 1984).
b. Contaminant Removal by Plain Sedimentation. Properly designed and
operated confined disposal areas can be extremely efficient in retaining
suspended solids and associated contaminants. This is especially true if the
dredging is conducted in a saltwater environment as is the case for
Commencement Bay. Palermo (in preparation) found that retention efficiency
for suspended solids in three saltwater disposal areas was above 99.9 percent
(inflow solids concentrations on the order of 100 g/1 and effluent suspended
solids concentrations on the order of tens of mg/1). Similar high retention
of the total concentration of metals was observed, varying from 84.5 to 99.9
percent. These data are in agreement with Hoeppel, et al. (1978), and other
investigators. Hoeppel, et al. (1978), described similar retention for
organics such as PCB and DDT which remain closely associated with particles.
Typical concentrations of various contaminants remaining in the effluent
following plain sedimentation are available in Hoeppel, et al. (1978), ahd
Palermo (in preparation), and are summarized in table 4-4.
4.03.03 Chemical Clarification.
a. Applicability. Chemical clarification is an effective treatment
method to remove turbidity, suspended solids, and adsorbed contaminants from
the effluent of a fine-grained dredged material containment area. The process
is used following plain sedimentation to reduce the required chemical dosage
and, therefore, the cost of treatment and to produce a higher quality effluent
than could be produced in a one-stage settling process (Schroeder, 1983).
However, chemical clarification is an ineffective method for removing soluble
contaminants.
The chemical clarification process can be adapted and simplified to perform
within the constraints of a normal disposal operation (Schroeder, 1983). In
this process, a liquid polymeric flocculant is fed into the effluent from the
primary containment area at the weir structure. The weir structure and
4-17
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discharge culvert are used to provide the required mixing without mechanical
equipment. A small secondary containment area is used for settling and
storage of the treated material, eliminating the need for a clarifier and
sludge handling equipment. However, a mud pump may be used to pump the
settled, treated material back into the primary containment area and to reduce
the required size of the secondary containment area. A sketch of the treat-
ment process is shown in figure 4-3.
Liquid polymeric flocculants are much simpler and less expensive to use than
inorganic coagulants such as ferric chloride and alum (Wang and Chen, 1977).
The treatment system described above is also less expensive than a conven-
tional system requiring a flash mixer, flocculation basin, clarifier, and
sludge handling equipment (Schroeder, 1983; and Jones, et al., 1978).
b. Limitations. Chemical clarification must follow plain sedimentation
and will not appreciably remove soluble and volatile contaminants.
c. Removal Efficiency. Chemical clarification, as applied here, can
remove up to 95 percent of the suspended solids and achieve an effluent
quality of 25 mg/1 suspended solids (Schroeder, 1983). Adsorbed contaminants
are reduced in proportion to suspended solids removal.
4.03.04 Filtration. Filtration is a treatment process used to provide addi-
tional removal of suspended solids and sediment-bound contaminants following
plain sedimentation and chemical clarification. The process has been adapted
to dredging operations through the use of pervious dikes and sandfill weirs
(Krizek, et al., 1976).
a. Pervious Dikes. Pervious dikes should use coarse-grained deep beds
that have low clarification efficiency per unit depth but maintain high perme-
ability throughout the filter life. The dike must not face clog or lose its
ability to achieve the required clarification. Example pervious dikes are
shown in figure 4-4. Typically, the dikes are 6 to 10 feet high and the
filter medium is coarse sand (Krizek, et al., 1976; and Culp, et al., 1978).
b. Sandfill Weirs. Sandfill weirs consist of several cylindrical or
rectangular cells that contain the filter medium and provide filtration in a
vertical gravity flow. Sandfill weirs are much more flexible than filter
dikes allowing easier replacement and maintenance. Example sandfill weirs are
shown in figure 4-5. The depth of the filter medium is generally kept as deep
as possible to provide better solids retention. The filter medium is
generally sand with a particle size of about 1 milimeter (mm) (Krizek, et al.,
1976).
c. Limitations.
(1) Pervious Dikes. If the system malfunctions, corrective measures,
if at all possible, are extremely expensive. The water to be treated should
have less than 1.0 g/1 suspended solids. The filter medium should be care-
fully selected to remove the suspended solids deep inside the fiter and not at
the face to prevent clogging and loss of efficiency (Krizek, et al., 1976).
4-18
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POLYMER FEED
SYSTEM
SECONDARY
CONTAINMENT
AREA
WATER
DREDGE
PIPE
WATER
FLOW
PRIMARY
CONTAINMENT
AREA
WEIR
BOXES
DISCHARGE
CULVERT
Figure 4-3: Schematic of Chemical Clarification Facility
4-19
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PROTECTIVE
LAYER
COARSE GRAVEL
3*(S?
/fi/A/l
FILTER MEDIUM
FOUNDATION
SOIL
IMPERVIOUS
MATERIAL
FINE GRAVEL
.»v;t 'P
- f '-'i vi •i'-'sV/KV-.J
m Mr fly* //
(a) HOMOGENEOUS SECTION
(b) STRATIFIED SECTION
Figure 4-4: Pervious Dikes
•VvfVi-
^ m wf mi wiwm
> ///^/^//
(c) BAFFLED SECTION
4-20
-------
t
* j FILTER MEDIUM
GRADED GRAVEL
COARSE STONE
M/a/a, FOUNDATION SOIL
/ \
i®l,
(c) DOWNFLOW CARTRIDGE
EFFLUENT
/ DISCHARGE
TROUGH
(a) DOWNFLOW WEIR
STOP —
LOGS
EFFLUENT
f DISCHARGE
i—1 TROUGH
/
(b) UPFLOW WEIR
INFLUENT
GUIDE H
\
"X
iii ft
wm
1
(d) UPFLOW CARTRIDGE
Figure 4-5: Sandfill Weirs
4-21
-------
(2) Sandfill Weirs. Sandfill weirs require excessive maintenance if
the influent contains more than 1 g/1 suspended solids (Krizek, et al., 1976).
d. Removal Efficiency. The filtration process can remove 60 to 98 per-
cent of the suspended solids and sediment-bound contaminants. Typically, the
effluent suspended solids concentration is reduced to 5 to 10 mg/1 in these
coarse filters.
4.03.05 Chemical Precipitation.
a. Applicability. Chemical precipitation by lime addition can signifi-
cantly reduce the total and soluble concentrations of many heavy metals. The
pH is raised to above pH 11 forming insoluble metallic hydroxides from the
soluble heavy metal species. This process may replace chemical clarification
in a treatment scheme. Chemical precipitation follows plain sedimentation and
precedes filtration. This process has been widely employed in water and
wastewater treatment but has not been examined and adapted for full-scale
dredging operations.
b. Limitations. The removals are limited by the solubility of the
hydroxide form of the heavy metals and the precipitate removal. Some species
of heavy metals are not removed by lime addition. Removals are improved if
the process is followed by filtration. The effluent pH must be lowered before
discharging the water.
c. Removal Efficiency. Chemical precipitation by lime addition can
remove as much as 99.9 percent of certain metals while removing less than
10 percent of other metals such as arsenic. Refer to table 4-5 for removal
efficiencies of specific metals.
4.03.06 Carbon Adsorption.
a. Overview. Carbon adsorption removes contaminants from water by
contacting the stream with a solid, activated carbon adsorbent in granular
(most common) or powdered form. Organic compounds and some inorganic species
become bound to the surface of the carbon particles (adsorption) and are
subsequently removed along with the adsorbent.
Carbon adsorption is normally used to remove organic compounds from municipal
effluents after biological treatment. The combination of the two processes
appears to be a cost effective method for removal of a wide range of organics
from aqueous wastes.
Several commercial carbons are available. The products differ in physical
properties such as pore size, surface area, and adsorption characteristics.
Some commercial carbons are listed in table 4-6. Carbon selection requires
laboratory testing of carbon adsorption capacities for the specific waste
stream to be treated. Both equilibrium adsorption isotherms and carbon column
breakthrough curves should be determined.
4-22
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TABLE 4-5
REMOVAL OF HEAVY METALS BY LIME COAGULATION AND RECARBONATION
Metal
Reference
Concentration
Before Treatment
mgll
Concentration
Alter Treatment
mgll
Final
pli
% Removal
Antimony11
5
11
90
Arsenic"
5
11
<10
18
23
23
9.5
0
Barium3
5
-1.3 (sol)"
11
Bismuth11
5
.0002 (sol)
11
Cadmium
9
Trace
11
-50
10
0.0137
0.00075
>11
94.5
Chromium ( + 6)
10
0.056
0.050
>11
11
Chromium ( + 3)
11
7,400
2.7
8.7
99.9'
18
15
0.4
9.5
97
Copper
11
15,700
0.79
8.7
99.9 *
12
7
1
8
86
12
7
.05
9.5
93
13
302
Trace
9.1
99'
16
15
0.6
9.5
97
Gold"
5
c.OQl (sol)
11
90 ^
Iron
13
13
2.4
9.1
82
14
17
0.1
10.8
99*
14
2.0
1.2C
10.5
40
Lead3
5
—
<.001 (sol)b
11
90'
18
15
0.5
9.5
97
Manganese
14
2.3
<0.1
10.8
96
14
2.0
l.lc
10.5
45
15
21.0
0.05
9.5
95
Mercury"
5
Oxide soluble
<10
Molybdenum
9
Trace
—
8.2
-10
18
11
0
9 *S
1«
Nickel
11
160
0.08
8.7
99.9*
12
5
0.5
8.0
90
12
5
0.5
9.5
90
IB
100
1.5
10.0
99
18
16
1.4
9.5
91
Selenium
10
0.0123
0.0103
>11
16.2
Silver
10
0.0546
0.0164
>11
97
Telluriumad
5
(<0.001 ?)
11
(?90+)
Titanium"-*1
5
(<0.001?)
11
(?904)
Uranium'
5
?
?
Zinc
5
.007 (sol)
11
90f
18
17
0.3
9.5
98
'The potential removal of these metals were estimated from solubility data.
"Barium and lead reductions and solubilities are based upon the carbonate.
'These data were from experiments using iron and manganese in the organic form.
"Titanium and tellurium solubility and stability data made the potential reduction estimates unsure.
'Uranium forms complexes with carbonate ion. Quantitative data were unavailable to allow determination of this effect.
Reference: Culp and Culp, 1974
4-23
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TABLE 4-6 a
PROPERTIES OF SEVERAL COMMERCIALLY AVAILABLE CARBONS
ICI
CALGON
WESTVACO
AMERICA
FILTRASORB
NUCHAR
WITCO
HYDRODARCO
300
WVL
517
PHYSICAL PROPERTIES
3000
(Bx30)
(8x30)
(12x30)
Surface area, m^/gm (BET)
600-650
950-1050
1000
1050
Apparent density, gm/cc
0.43
0.48
0.48
0.48
Density, backwashed and drained.
Ib/cu ft
22
26
26
30
Real density, gm/cc
2.0
2.1
2.1
2.1
Particle density, gm/cc
1.4-1.5
1.3-1.4
1.4
0.92
Effective size, mm
0.8-0.9
0.8-0.9
0.85-1.05
0.89
Uniformity coefficient
1.7
1.9 or less
1.8 or less
1.44
Pore volume, cc/gm
0.95
0.85
0.85
0.60
Mean particle diameter, mm
1.6
1.5-1.7
1.5-1.7
1.2
SPECIFICATIONS
Sieve size (U.S. std. series)
Larger than No. 8 (max. %)
8
8
8
c
Larger than No. 12 (max. %)
c
c
c
5
Smaller than No. 30 (max. %)
5
5
5
5
Srrtaller than No. 40 (max. %)
c
c
c
c
Iodine No.
650
900
950
1000
Abrasion No., minimum
b
70
70
85
Ash (%)
b
8
7.5
0.5
Moisture as packed (max. %)
b
2
2
1
a Other sizes of carbon are available on request from the manufacturers,
b No available data from the manufacturer,
c Not applicable to this size carbon.
Source: ADL, 1976
4-24
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b. Carbon Columns. Carbon columns can be used in either upflow or down-
flow configuration and can be arranged in either series or parallel operation
as shown in figure 4-6. Downflow is generally an inefficient use of activated
carbon and will require frequent backwashing. Upflow beds usually operate in
expanded bed mode requiring no backwashing, but may require pressure pumping
and will cost more than downflow beds. Field loading rates vary from 2 to 10
gallons per minute (g.p.m.) per square foot of bed cross section. Bed depths
range from 4 feet to 20 feet. In a pulsed bed system, a layer of exhausted
carbon is withdrawn from the bottom of the carbon bed with a regenerated layer
being added to the top of the bed.
c. Powdered Carbon. Powdered carbon is fed to a treatment system using
chemical feed equipment. The spent carbon may either be wasted or recovered
and regenerated. Carbon requirements range from 250 to 350 pounds of carbon
per million gallons of water treated. It is conceivable that powdered carbon
could be added to the secondary settling basin with chemical addition during
the chemical clarification process. The carbon would adsorb organics and
trace metals and could be pumped back to the plain sedimentation basin along
with the rest of the flocculated solids.
d. System Configuration and Efficiencies. The choice of system con-
figuration for both granular and powdered carbon depends on many factors.
Table 4-7 presents a summary of the primary determinants. The flow direction
depends on the specific application. Downflow systems can accommodate higher
suspended concentrations (i.e., 65 to 70 mg/1) if the liquid viscosity is
similar to that of water. Solids are filtered out and the column requires
periodic backwashing. Upflow systems can handle more viscous liquids and
require less bed washing. The most commonly used contact method is a flow
through column system.
Carbon adsorption technology is applicable to dissolved organics, generally.
Many organics can be reduced to the 1 to 10 ug/1 level. Results of an EPA
study showed that 51 of 60 toxic organic compounds could be removed (EPA,
1980). Some inorganic species, such as antimony, arsenic, bismuth, chromium,
tin, silver, mercury, and cobalt, are partially adsorbed (EPA, 1982). A list-
ing of the potential for removal of inorganic material by activated carbon is
given in table 4-8. Conventional water quality parameters (BOD, COD, TOC) are
also reduced by carbon adsorption; the performance level is dependent on the
specific waste stream characteristics. Although there is no theoretical,
technical upper limit for the concentration of adsorbable organics in the
waste stream, economics in conventional systems generally dictate a practical
limit of about 1 percent.
e. Carbon Regeneration. If carbon usage rates exceed 1,000 pounds per
day, regeneration of carbon is generally feasible. Regeneration of spent
carbon may be accomplished by a variety of means, the most common involving
thermal destruction of the adsorbed organics in a multiple hearth furnace.
About 5 to 10 percent of the carbon is lost in this regeneration process (and
most other processes) due to the creation of fines from the mechanical handling
of the carbon. Other regeneration processes include thermal treatment with
steam, extraction of adsorbed organics with solvents (including acids, bases,
and super critical fluids) , and biological degradation of the adsorbed
material.
4-25
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MOVING BED
DOWN FLOW IN SERIES
OUT
IN
IN
OUT
• COUNTER-CURRENT CARBON USE
• PRIOR SUSPENDED SOLIDS REMOVAL
• SMALL VOLUME SYSTEMS
• COUNTER-CURRENT CARBON USE
• MAXIMUM LINEAR VELOCITY
• LARGE VOLUME SYSTEMS
DOWN FLOW IN PARALLEL
UPFLOW-EXPANDED IN SERIES
IN
OUT
OUT
IN
• FILTRATION AND ADSORPTION
CAPABILITY
• MAXIMUM LINEAR VELOCITY
• LARGE VOLUME SYSTEMS
• COUNTER-CURRENT CARBON USE
• MINIMUM HEAD LOSS
• MINIMUM PRETREATMENT
Figure 4-6: Granular Activated Carbon System Configuration
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TABLE 4-7
CONTACTING SYSTEMS
Method
Application Conditions
Comments
Single or parallel adsorbers
Pollutant breakthrough curve is steep.
Typical flows are 1 to 4 gpm/ft^.
Carbon recharge Interval is long.
Volume flow Is high.
Parallel system is usually selected if
pressure drop problems are expected for
the system.
Influent Is viscous.
Moderate adsorbent expense.
Adsorbers In series
Pollutant breakthrough curve is gradual.
Typical flows are 3 to 7 gpm/ft^.
Uninterrupted operation is necessary.
High adsorbent expense.
Relatively low effluent concentration is required.
Carbon recharge interval is short.
Expanded upflow adsorber(s)
For high flows and high suspended solids
concentrations.
Typical flows are 5 to 9 gpm/ft^.
Suspended solids are passed through the
column and not separated.
Moving Bed
For systems requiring efficient use of carbon
(i.e., carbon adsorption capacity is exhausted
before removal from column).
Influent must contain less than 10 mg/1
TSS, and not biologically active. Either
parameter will cause a pressure drop in the
system and necessitate removal of carbon
prior exhaustion of its absorption capacity.
Powdered carbon with subsequent
clarifler and/or filter
Carbon usage higher than for series of fixed-bed
adsorbers.
Ko restrictions on suspended solids or oil
and grease in influent.
Influent concentration of pollutants should be
relatively constant to avoid frequent sampling
and adjustment of carbon dosage.
Capital equipment costs relatively low.
Simple to operate.
Powdered activated carbon with
activated sludge
For activated sludge systems receiving toxic or
shock organic loadings.
Protects the biological system from toxic
organics and shock loadings. Generally
improves effluent quality.
Source: ADL, 1976.
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Table 4-8
POTENTIAL FOR REMOVAL OF INORGANIC MATERIAL BY ACTIVATED CARBON
Constituents
Metals of high sorption potential:
Antimony
Arsenic
Bismuth
Chromium
Tin
Potential for Removal by Carbon
Highly sorbable in some solutions
Good in higher oxidation states
Very good
Good, easily reduced
Proven very high
Metals of good sorption potential:
Silver
Mercury
Cobalt
Zirconium
Reduced on carbon surface
CH^HgCl sorbs easily, metal
filtered out
Trace quantities readily sorbed
possibly as complex ions
Good at low pH
Elements of fair-to-good sorption potential:
Lead Good
Nickel Fair
Titanium Good
Vanadium Variable
Iron FE3+ good, FE^+ poor, but may
oxidize
Elements of low or unknown sorption
Copper
Cadmium
Zinc
Beryllium
Barium
Selenium
Molybdenum
Manganese
Tungsten
Slight, possible good if complexed
Slight
Slight
Unknown
Very low
Slight
Slight at pH 6-8, good as complex
ion
Not likely, except as MnO^
Slight
Miscellaneous inorganic water constituents:
Phosphorus
P, free element
3-
PO^ phosphate
Free halogens:
F2 fluorine
CI2 chlorine
Br2 bromine
I2 iodine
Not likely to exist in reduced
form in water
Not sorbed but carbon may induce
precipitation Ca3(PO^>2
Will not exist in water
Sorbed well and reduced
Sorbed strongly and reduced
Sorbed very strongly, stable
Halides
F~ flouride
CI", BR", I"
4-28
May sorb under special conditions
Not appreciably sorbed
-------
f. Limitations. Carbon adsorption system performance is sensitive to the
composition of the influent and flow variations. Because a system design
based on good data can perform poorly if influent conditions change, systems
are generally oversized. For fixed bed, granular carbon systems, special
attention must be given to the materials of construction (to prevent corrosion
and mechanical failure) and to the materials handling equipment (pipes, pumps,
valves, controls) for the transfer of carbon to and from various tanks and/or
regeneration units.
Care must be taken to ensure that the adsorption capacity of the carbon is not
reduced either by chemicals, resins, or fine precipitates in the influent or
by the continued presence of similar chemicals in the residual water (after
draining) if the carbon is thermally regenerated. In the latter case, any
material (e.g., inorganic salts, some resins) that are not volatilized or
combusted during regeneration will remain in the pores of the carbon resulting
in an irreversible loss of adsorption capacity.
In all cases, it is prudent to consider the possibility of biological activity
in the carbon system. Such activity can help (via pollutant biodegradation)
or hinder (via clogging and/or odor generation) the process. Suspended solids
and oil/grease can interfere with carbon adsorption treatment. Influent
concentrations of these pollutants should not exceed 50 ppm and 10 ppm,
respectively (ADL, 1976).
Treatment of highly saline waters has the potential of resulting in insoluble
salt formation during carbon regeneration. Rinsing spent carbon with fresh-
water prior to regeneration should prevent this potential problem. Site-
specific design studies will indicate if carbon regeneration is appropriate
and if freshwater washing is needed.
4.03.07 Ozonation.
a. Overview. In ozonation, contact with ozone, a powerful oxidizing
agent, breaks down many refractory organic compounds not treatable with
biological treatment techniques. Ozone, produced in a separate generator, is
introduced to a contactor where it mixes with the wastes and reacts with
oxidizable species present.
Ozone dose rate is usually expressed as either ppm ozone or pounds of ozone
per pound of stream contaminants treated. Typical dose rates are 10 to 40 ppm
for the former and 1.5 to 3.0 pounds per pound of contaminant removed for the
latter (ADL, 1976). Retention time ranges from 10 minutes to 1 hour in
several stages.
Typically, the very high ozone to waste ratios are encountered in potable
water facilities where the influent contaminant concentrations are in the ppb
range and the effluent concentrations are nondetectable.
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b. Effectiveness. Ozonation is applicable only to dilute wastes,
typically containing less than 1 percent oxidizable materials. The destruc-
tive power to refractory compounds may be enhanced by combining ozonation with
ultraviolet radiation (Prangle, et al., 1975). Ozonation is effective with:
o chlorinated hydrocarbons,
o alcohols ,
o chlorinated aromatics,
o pes ticides, and
o cyanides.
Large contactors are required because reaction rates are mass transfer
limited; ozone has only limited solubility in water. Contactor depth is
typically on the order of 5 m (16 feet) to ensure adequate mixing and reaction
time. Ultraviolet lamps, if used, are operated within the contactor vessel.
c. Limitations. Ozone is corrosive, requiring special construction
materials. Suitable materials include:
o stainless steel,
o unplasticized PVC,
o aluminum,
o teflon (registered trademark), and
o chromium-plated brass or bronze.
Ozone is acutely toxic; personnel safety is therefore a major concern. Modern
systems are completely automated. An ozone monitor measures ozone levels in
the gaseous effluent and reduces the ozonator voltage or frequency if gaseous
levels exceed a pre-set limit (usually 0.05 ppm). An ambient air monitor
sounds an alarm and shuts off the ozonator in the event of leaks of ozonized
air. An off-gas ozone destruction unit is also generally used in modern
systems.
4.03.08 Dissolved Solids Removal Systems.
a. Overview. There are a number of processes that can be applied to the
treatment of brackish and highly saline waters. These processes include, but
are not limited to, distillation or evaporation, electrodialysis, ion exchange,
and reverse osmosis. In the case of nearshore and upland treatment, these
processes would only be used to achieve the highest quality of water. Because
of the high initial investment and intensive energy and operation require-
ments, dissolved solids removal is rarely used except in production of potable
4-30
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drinking water or high quality water for industrial operations. There have
been no known applications of dissolved solids removal associated with any
dredging operation.
b. Distillation. Distillation or evaporation of saline water to produce
freshwater goes back to antiquity. In distillation or evaporation processes,
pore water vapor is created by heating saline water. The vapor is separated
from the saline water and is condensed to form pure water.
There are three principal types of distillation processes currently being used
on new construction. These are:
o long-tube vertical (LTV),
o multistage flash (MSF), and
o vapor compression (VC).
In LTV distillation, the water to be vaporized flows by gravity down the
inside of a long vertical tube, while steam or hot vapor supplies heat on the
outs ide.
In MSF distillation, the water is heated under pressure in tubes and then
allowed to expand suddenly or "flash" into a chamber. As some of the water
evaporates or flashes, the remaining water cools slightly and then flows into
another chamber at lower pressure where it flashes again. The flashed vapor
condenses on the outside of the tubes in each chamber through which cooler
water is flowing and picking up heat. The condensed pure water then drips
into collecting pans and is pumped to service.
In VC distillation, pure water vapor, which has been evaporated at a tube
surface or in a flash chamber, is mechanically compressed (usually by a
centrifugal or axial flow gas compressor) to raise its temperature and
pressure for use in vaporizing more water. VC cycles must utilize mechanical
or electrical energy or work rather than heat as the primary energy input for
distillation.
These distillation processes can be combined and there are many individual
modifications, depending upon the amount, type, and cost of available steam,
power, water, and other basic factors.
c. Electrodialysis. Today, electrodialysis (ED) is a widely used process
for the treatment of brackish or highly mineralized waters. In ED, salts and
minerals are removed from a stream of saline water through special plastic
membranes by the action of a direct electrical current. The salts and
minerals pass through the membranes in the form of positively and negatively
charged ions. The water from which these ions have been removed flows between
the membranes and is collected as a partially demineralized product via
manifolds cut through the membranes. The salts and minerals removed from the
product stream pass through the membranes into another stream of water which
4-31
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continuously washes the other side of each membrane and emerges through mani-
folds as a more concentrated waste stream. ED can operate at low pressures
(approximately 50 psi).
d. Reverse Osmosis. Over the past decade, very thin membranes have been
synthesized from cellulose acetate, and more recently from nylon, that pass
relatively pure water and retain relatively salty water when a saline water is
forced against them by high pressure. This filtration-like process is
generally referred to as reverse osmosis (RO).
R0 units of different types and sizes have been built and operated for various
periods since the early 1960's. Most units have ranged from laboratory scale
to a few thousand gallons per day. Several units in the 50,000- to 100,000-gpd
range have been assembled, but significant field data or field experience are
not yet available on these larger units.
e. Effectiveness.
(1) Distillation. Distillation can result in 99+ percent removal of
contaminants. Distillation plants having capacities up to several million
gallons per day are in operation at a number of locations throughout the world
and have proven their reliability.
(2) Electrodialysis. ED plants having capacities up to about
1 million gallons per day are in operation at a number of locations throughout
the world and have proven their reliability to produce freshwater for utility
use. Removal of inorganics is very high (90+ percent).
(3) Reverse Osmosis. RO is capable of removing greater than 90 per-
cent of total dissolved solids (TDS) from wastewater streams containing up to
50,000 mg/1 TDS. Organics with molecular weight in excess of 300 to 500, such
as pesticides, can be removed at efficiencies exceeding 90 percent. Operation
is sensitive to wastewater pH, total suspended solids levels, and TDS levels.
f. Limitations.
(1) Distillation. Distillation plants require substantial amounts of
thermal energy or electrical power. Accordingly, the cost and availability of
energy are important factors in both the design and economic feasibility of
distillation plants.
Close attention to water chemistry is essential to maintain the vital heat
transfer surfaces of distillation equipment at peak efficiency. The chemistry
and biochemistry of seawater vary substantially at different locations and
expert advice should be sought on the optimum chemical and mechanical treat-
ments and operating conditions to avoid excessive corrosion, hard scale
formation, or marine fouling.
(2) Electrodialysis. ED plants require clear waters free from iron,
manganese, turbidity, and organic matter for optimum operations. Accordingly,
pretreatment of water by conventional means is always required prior to ED
4-32
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plants operating on surface water. ED plants will generally require from 10
to 30 percent of the feed water to carry off the concentrated salts and
minerals removed.
(3) Reverse Osmosis. Certain problems of the RO field are under
intensive study and development. Pretreatment is often required to handle the
following condition:
o Leachate Variability. Rapidly changing leachate properties such as
pH, temperature, and suspended solids concentration can limit membrane life
requiring frequent replacement. Leachate equalization prior to the RO treat-
ment should be considered if highly variable conditions exist.
o Leachate pH. Because membrane operation is limited to certain pH
ranges, pH adjustment should precede RO operation if necessary.
o Biological Organisms. Living organisms in leachate can form films
on RO membranes which reduces permeability. Such organisms should be destroyed
by chlorination or ozonation prior to RO treatment.
o Total Suspended Solids (TSS). TSS can plug RO modules, parti-
cularly the hollow fiber type. Suspended solids should be minimized to
particle sizes less than about 10 microns prior to introduction in most RO
modules.
4.03.09 Stripping.
a. Overview. Stripping removes volatile contaminants from an aqueous
waste stream by passing air or steam through the wastes. With air, the
volatile, dissolved gases are transferred to the air streams for treatment
such as carbon adsorption or thermal oxidation. With steam the process is, in
essence, a steam distillation of the waste with the volatile contaminants
ending up in the distillate for treatment. Typical system configurations are
shown in figures 4-7 and 4-8.
b. Effectiveness. Both versions of stripping are capable of high removal
efficiencies. Air stripping of ammonia from wastewaters has exceeded 90 per-
cent for influent ammonia concentrations of less than 100 ppm (ADL, 1976), and
99+ percent has been achieved for removal of trichloroethylene from ground
water. Steam stripping can be applied to:
o volatile organic compounds (phenol, vinyl, chloride, etc.);
o water-immiscible compounds (chlorinated hydrocarbons, etc.);
o ammonia; and
o hydrogen sulfide.
Removal efficiencies of volatile organic compounds from wastewaters ranging
from 10 percent to 99 percent have been reported (EPA, 1980).
4-33
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AIR OUTLET
WATER
INLET
AIR
INLET
WATER
OUTLET
WATER
NLET
DRIFT
ELIMINATORS
AIR
INLET
COLLECTION BASIN
CROSS-FLOW TOWER
FAN
AIR
OUTLET
WATER
INLET
DRIFT
»»»»»)»»»»f eliminators
"vv
AIR
INLET
'II
\
_D-
:fill;
JLJ-
DISTRIBUTION
SYSTEM
AIR
INLET
WATER
COLLECTING
BASIN
COUNTERCURRENT TOWER
Figure 4-7: Air Stripping Towers
4-34
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CONDENSER
WATER
CONCENTRATED
VAPORS
CONDENSATE
TANK
STEAM
Figure 4-8: Typical Steam Stripping System
4-35
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c. Limitations. Air stripping has been demonstrated only for ammonia in
cooling tower systems. Both air and steam stripping pose potential air pollu-
tion problems if volatile organic compounds are present in the leachate. Air
pollution problems can be prevented by using emission control devices (e.g.,
condenser, carbon adsorption filters) and maintaining proper operating
conditions in the system.
4.03.10 Ion Exchange.
a. Overview. The ion exchange (IE) removes dissolved materials from
aqueous solution by using specialized, insoluble organic or inorganic com-
plexes known as zeolites or synthetic organic resins. In IE, substances to be
removed from solution are ionized and then exchanged at cationic and anionic
exchangers. Therefore, IE is effective mostly for nutrients, metals, and
simple anions (e.g., sulfate, nitrate). Following filtration to reduce
suspended solids, the effluent is passed downflow through the ion exchange bed
until the bed reaches the point of exhaustion; afterwards, the exhausted bed
can be regenerated. The discharge from the regeneration process is called
spent regenerant. It amounts to 2.5 to 5 percent of the effluent stream and
requires some form of processing for separation of removed ions so that the
regenerant can be reused. The alternative processes available for regenerant
recovery are air stripping or steam stripping at high pH and electrodialysis
treatment (EPA, 1978).
The process for individual beds is batch, but by using multiple beds,
continuous operation can be accomplished.
b. Effectiveness. Most inorganic dissolved salts and some organic
dissolved salts can be removed by ion exchange. Ion exchange exhibits high
ammonia ion removal efficiency; 93 to 97 percent. It is not significantly
impaired by temperature fluctuation and unaffected by toxic compounds.
Residual ammonium ion concentrations are in the range of 1 to 3 mg/1 (EPA,
1978). Performance on other volatiles has not been well documented. Very few
installations using large scale ion exchange have been built.
c. Limitations. Theoretically, ion exchange processes are capable of
treating TDS concentrations up to 10,000 to 20,000 mg/1. However, practical
operations are limited to TDS concentrations less than 2,500 mg/1 because of
excessive service requirements associated with resin regeneration at higher
TDS concentrations.
Ion exchange will only remove specific ions according to resin selection,
limiting its usefulness for broad spectrum inorganics removal. Ion exchange
is a multistep process requiring use of large amounts of acids and alkalies,
precise chemical control to assure economy, and either removal of solid resins
or frequent switching of streams. Ion exchange processes thus present more
problems in reliability and control than the more continuous thermal or
electrical processes.
In the event of human or mechanical errors, the feeding of any form of alkali
into the type of saline waters found in most of the United States will result
in a high probability of hard scale deposition.
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4.04 Runoff and Leachate Treatment.
4.04.01 Overview. Runoff water and leachate produced at the disposal site
will vary in quantity and contaminant concentration over time. Runoff water
will be produced initially as the site dewaters. During this time period, it
can be expected to have a higher contaminant concentration than the runoff
water resulting from precipitation after a surface cap has been placed.
Leachate from the site will be produced as water percolates through the cover
or cap and the inplace dredged material. Although the quantity of the
leachate produced will be relatively small, the contaminant concentrations may
be high and leachate production will probably persist for the life of the site.
Available data for the characterization of leachate produced from dredged
material is very limited. Yu and Chen (1978) found that potential adverse
water quality impacts most likely will be caused by the increases of chloride,
potassium, sodium, calcium, total organic carbon, alkalinity, ion, and manga-
nese. Field monitoring also detected low concentrations of cadmium, copper,
mercury, lead, zinc, phosphate, and nickel. The extent of the potential
impact was related to the dredged material's physiochemical properties, site
specific ground water hydrogeological patterns, and environmental conditions
of the surrounding area. Yu and Chen concluded from trace metal analysis that
manganese and iron should pose the greatest water quality problems in upland
dredged material disposal. However, leachate quality from dredged material
will be highly site specific. Since the data available for dredged material
leachate is limited, the remainder of this discussion will concentrate on the
treatment of landfill leachate. Landfill leachate will often be of lesser
volume and higher concentrations of contaminants than dredged material
leachate. As such, dredged material leachate can be expected to be more
difficult to monitor and treat than landfill leachate. However, the latter
represents the best analogy available for leachate from dredged material.
Depending on the quantity and quality, runoff water can be treated as either
as site effluent (4.03 above) or as leachate (4.04.02 below).
4.04.02 Treatment of Landfill Leachate. The treatment alternatives for
landfill leachate can be divided into two categories: off-site and on-site
treatment. Offsite treatment can be accomplished simply by the addition of
leachate to a municipal wastewater treatment plant stream. Wastewater treat-
ment plants are not adversely affected by accepting up to 2 to 5 percent by
volume of high strength leachate (Shafer, 1983). Normally a sewer surcharge
charge would be required. The option of utilizing a nearby industrial waste
treatment plant is also a viable alternative. Although treatment fees can be
significant, the reduction of the need for onsite personnel and treatment
facilities makes the use of nearby municipal or industrial wastewater treat-
ment facilities an attractive option. This off-site treatment option should
be explored for upland sites.
The array of on-site treatment systems used in leachate treatment parallel
those commonly in use for wastewater treatment and can be classified as either
physical-chemical or biological treatment systems.. Due to the wide variation
in the composition and biodegradability of leachates from different waste
4-37
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types, no single treatment process or combination of processes can be recom-
mended as optimum for all circumstances. Selection of the best treatment
process requires knowledge of the quality and quantity of leachate to be
treated and the specific discharge requirements of the site. Treatment
systems currently adequate may, due to changes in leachate composition during
aging of the landfill or regulatory revisions, be inadequate at some future
time. Fluctuations in leachate quality and strength can cause serious
problems in maintaining an active biomass for biological treatment or in
attempts to automate chemical treatment systems.
a. Biological Treatment. Both aerobic and anaerobic systems have been
given extensive bench scale study and both have been found to be effective in
removing organics and other constituents from landfill leachates (Shafer,
1983). Full scale treatment systems have almost exclusively used aerobic
conditions. In general, conventional activated sludge systems do not work
satisfactorily with high strength leachates, making dilution with clean water
at the site a requirement. Activated sludge systems studied have required
retention times of over 5 days to prevent system failure and to develop
maximal removal efficiencies. The only large-scale anaerobic leachate system
currently under study in the United States has not proved to be effective due
to the low level of biodegradable organic materials in the feed (Shafer, 1983).
Landfill leachate is usually found to be nutrient limiting in phosphorus so
that phosphate additions are often recommended to increase system efficiency
and reduce retention times. Heavy metal toxicity has not been shown to be a
problem in any system yet studied, but lime addition as a pretreatment has
been included in several studies to remove metals (Shafer, 1983).
b. Physical-Chemical Treatment. Carbon adsorption or reverse osmosis
appear promising for removal of refractory organics. Chemical precipitation,
or reverse osmosis may best be used for metal and total dissolved solids
removal. Lime addition in the final treatment stage was found to reduce
residual organics and metals in activated sludge effluent, but the lime
dosages were said to be so large as to be uneconomical. Effluent polishing by
carbon adsorption is also effective and may be more economical (Shafer, 1983).
Reports on the use of physical-chemical treatment systems on high COD leach-
ates have concluded that none were feasible unless preceded by biological
treatment to reduce the COD. Neither chemical precipitation (using lime or
sodium sulfite) nor chemical coagulation (using alum or ferric chloride) were
effective in removing oxygen demand. Chemical oxidation using chlorine,
hypochlorite, permanganate, or ozone were more effective; but, required
prohibitively expensive doses of oxidate for treating leachates (Shafer, 1983).
4.05 Disposition of Treatment Materials. With the exception of ozonation,
the treatment processes discussed in sections 4.03 and 4.04 do not destroy
contaminants, they simply concentrate them by removal from site effluent,
runoff or leachate waters. The concentrated contaminants, often contained in
a process sludge or regenerant fluid, must be disposed of in an appropriate
facility.
4-38
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If the sludge is sufficiently contaminated to be classified as dangerous (DW)
or extremely harzardous (EHW) waste, it will require handling and disposal as
specified in state and Federal regulations. However, in some cases, classi-
fication as DW or EHW may not preclude the basic and most common option: dis-
pose of treatment sludges or fluids in the primary disposal site. Disposing
of DW or EHW treatment materials in the primary disposal site would require
that the site be designed to receive these materials (most likely an upland
s ite).
After the primary site has been closed, treatment materials will need to be
transported to an approved disposal facility. As mentioned above, if an
industrial or municipal treatment facility is available to process the site
leachate, postclosure treatment sludges or fluids would not be a major site
consideration.
4.06 Biological Control of Disposal Areas.
4.06.01 Overview. Biological control of disposal areas, as discussed here,
refers to isolating contaminated sediments from direct contact with biological
organisms. In open-water disposal areas, biological control measures are
limited to capping of contaminated sediments and cap monitoring to ensure
sufficient thickness to avoid bioturbation of contaminated mate- rial. These
measures are discussed above.
For upland and nearshore disposal areas, biological control relates primarily
to the period of time after disposal of the contaminated sediments and prior
to placement of final surface cap. This period could involve several years,
as large disposal sites are frequently filled with materials from several
dredging cycles or jobs and over extended time frames. Additionally, sites
are frequently allowed to consolidate and dewater prior to placing final
surface finishing materials.
After dredged material has been placed in either a nearshore or an upland
environment, salt-tolerant plants can invade and colonize the site. In most
cases, fine-grained dredged material contains large amounts of nitrogen and
phosphorus, which tend to promote vigorous growth of plants on dredged
material placed in confined disposal sites at elevations that range from
wetland to upland terrestrial environments. In other cases, salt content of
the sediment may prevent plant growth for a period of months to a couple
years. There is potential for movement of contaminants from the dredged
material into plants and then eventually into the food chain.
Animals have also been known to invade and colonize confined dredged material
disposal sites. In some cases, prolific wildlife habitats have become
established on these sites. Concern has developed recently on the potential
for animals inhabiting either nearshore or upland confined disposal sites to
become contaminated and contribute to the contamination of food chains
associated with the site.
4-39
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4.06.02 Biological Control Measures. The first step in selecting appropriate
biological control measures is the identification of routes and the estimation
of rates of contaminant loss due to biological uptake. This information is
usually available from sediment testing conducted prior to disposal. The
biological control program should be designed in consideration of the poten-
tial exposure times, the bioavailability of the sediment contaminants, and the
amount and effect of potential uptake that is predicted.
Measures that can be implemented include:
a. fencing to prevent human and large mammal access to the site,
b. pest and plant control by application of biocides, and
c. periodic (daily to yearly) covering programs:
o roll-back grids to prevent small mammal burrowing,
o clean soil or sediment layers placed prior to inactive periods, and
o synthetic liners.
The simplest control measure is the placement of a surface cover thick enough
to protect against contaminant uptake in plants and animals. Other control
measures are discussed in section 4.02.03.
4.07 Monitoring and Remedial Response.
4.07.01 Purpose and Need. Containment and treatment do not guarantee con-
taminant isolation in the long term. Present state-of-the-art in disposal of
contaminated materials requires monitoring of containment success in order to
obtain an acceptable level of confidence. Monitoring parameters and frequency
will necessarily vary depending on types and levels of contamination and
existing resources and uses that might be impacted by contaminant release.
Standards are not available. For this reason, costs are not provided in this
report.
Even more important than what and when to monitor is how to respond to moni-
toring indications. Remedial response options will be substantially different
for each disposal method. The potential high cost of remedial response may
well make it worthwhile to over design the original containment and treatment
facility. Further technical guidelines may be found in state solid waste
regulations.
4.07.02 Monitoring Parameters and Frequency.
a* Open-Water. Contaminants can escape from a capped area by diffusion
through the cap, convection, and bioturbation. The most practical monitoring
measure is checking cap thickness and examining cap integrity. This is done
by both remote sensing (bathymetry) and direct sampling (with cores). Coring
would not disturb the cap integrity if the cap is comprised of clean sediments
4-40
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that will "self-heal" once the core is removed. Additionally, core samples
can provide indication of extent of bioturbation and movement of contaminants
through the cap#
Cap integrity should be checked at least four times annually for several years
until cap movement rates are established for a given site. After these are
determined, annual monitoring should suffice. Stability should also be
monitored after severe storms and upon completion of recent disposal and new
cap. Contaminant measurements in the core of the cap should be done annually.
b. Upland. Contaminants can escape from liners into ground water.
Therefore, observation wells are used to monitor ground water composition.
Figure 4-9 shows a typical monitor well network. Sampling of leachate from
the underdrains for analysis can be conducted concurrently with well sampling.
Diffusion and convection can cause loss of volatile gases through a cap. Gas
samples can be collected and analyzed to estimate this loss.
Upland ground water and leachate monitoring frequency depends upon ground
water use. If a nearby aquifer supplies drinking water, monthly sampling may
be warranted; otherwise, ground water and leachate samples taken four times
per year should be adequate. Air samples can be taken concurrently with water
samples.
c. Nearshore. Escape of soluble contaminants from the nearshore sites
would be more rapid than escape from the upland area due to close proximity to
and movement of water. Monitoring contaminant escape into adjacent waters is
very difficult and techniques have not been demonstrated in this environment.
Shellfish sampling around the site and tissue analysis may provide evidence of
contaminant escape. Alternately, placement of recoverable, adsorbent mate-
rials (cartridge filter) in a well within the containment dike would serve to
concentrate contaminants escaping the site and provide an integrated measure
of the contaminant loss (a proven ground water technology). Volatiles
monitoring could be done similarly to that for upland sites.
Monitoring should be done annually at first, taking into account seasonal
influences on organism bioaccumulation. Volatiles can be monitored four times
per year.
4.07.03 Remedial Response.
a. Open-Water. Cap integrity is maintained by addition of more capping
material.
b. Upland. First response to excessive loss of soluble contaminants
should be activation of leachate collection system and treatment of leachate.
Purified leachate can be discharged or reinjected into gravel bedding to
maintain positive ground water pressure. If the collection systems fails and
excessive ground water contamination appears, detailed site explorations are
necessary. These may lead to ground water treatment and/or sediment removal
from the disposal site.
4-41
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LEGEND:
A, B, C - MONITORING
WELLS
GROUND
WATER
FLOW
LANDFILL
LEACHATE PLUME
Figure 4-9: Leachate Plume Produced by Upland Landfill Above
Groundwater Table and Site Well Monitoring System—Plan View
4-42
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Volatiles loss via escape of gaseous phase can be retarded by placing a new
surface cap.
c* Nearshore. Stopping excessive leakage from nearshore sites could be
accomplished by: construction of a new closure berm, dewatering the space
between the berms and treatment of leachate collected; construction of slurry
walls within containment berms; corrective actions to reduce rainwater
infiltration at the surface (improve cap); and/or, moving sediment to another
s ite.
4-43
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CHAPTER 5.0 COSTS FOR DREDGING, DISPOSAL, CONTROL, AND TREATMENT
5.01 Introduction. This chapter summarizes available information concerning
costs of dredging, disposal, control, and treatment of contaminated sediments
in Commencement Bay. Costs for dredging and disposal of contaminated sedi-
ments are dependent upon the degree of contaminant containment desired. While
some cost information is available for specific dredge types, disposal sites,
and treatment methods, the costs of many potentially useful or important addi-
tions to these categories are not readily available. Therefore, cost estimates
for application to Commencement Bay are provided for relative comparison at
this stage of planning.
Table 5-1 summarizes the factors affecting costs for dredging, disposal, and
control in the Commencement Bay area; tables 5-2 through 5-8 provide the cost
estimates. For discussion, general principles affecting costs are described
in the beginning of each section and specific costs then follow. Descriptions
of the technology being discussed are found in the preceding chapters.
5.02 Dredging Costs.
5.02.01. General Cost Principles. The cost of dredging per unit volume is
extremely variable. For example, the cost of mobilizing a dredge will vary
with equipment availability and will be amortized into the quantity of mate-
rial being dredged. As the distance between the disposal site and dredging
location increases, the requirement for additional barges, pipeline booster
pumps, or hopper downtime will affect cost. Production rates, which can vary
greatly for different equipment, physical sediment characteristics, and site
conditions, also will affect cost. However, the traditional considerations of
production rates and cost must be considered in reference to the objective of
efficient removal of contaminants. In some cases, operational conditions that
maximize production rates will also improve contaminant confinement (e.g.,
high solids concentrations for pipeline dredging). In other cases, improved
production will result in greater contaminant loss (e.g., hopper dredge
overflow).
The dredges themselves are for the most part comparably priced and do not
account for most of the cost variability. However, job specific factors can
produce substantial cost differences between dredge types. Many of the
dredges described are readily available for use in Commencement Bay. The
notable exception is the group of special-purpose dredges for which
availability could be a major cost factor to be considered.
5.02.02. Hydraulic Dredges.
Cutterhead. Hydraulic pipeline cutterhead dredges generally have the
widest range of application of dredge types and are usually also among the
least expensive methods. Their widespread use and availability is an impor-
tant cost factor. There are many cutterhead dredges available in the North-
west. Conventional cutterhead dredges are not self propelled but require
towboats to move them between dredging locations. Thus, mobilization and
setup are major and costly undertakings. A large dredge can cost between
5-1
-------
TABLE 5-1
COST FACTORS CHECKLIST
Dredging
Dredge type and equipment modifications
Equipment mobilization and demobilization
Transport distance and vertical lift
Transport method
Production rate
Operational modifications
Disposal
Site acquisition
Site information needs
Site preparation
Discharge controls (weirs, vertical diffuser)
Control and Treatment
Flow rate
Level and type of treatment
Treatment end-products management (e.g., sludge disposal)
Monitoring
Types of monitoring
Frequency of monitoring
Duration of monitoring
Remedial response to monitoring indications
5-2
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TABLE 5-2
TYPICAL DREDGE CHARACTERISTICS AND COSTS I/
Size or
Production
Capacity
Rate (c.y./hr)
Cost Per Cubic
Cutterhead2/
6
71
5.00
8
79
4.50
10
225
4.00
Pipe line
12
405
3.50
Diameter
14
525
2.15
(Inche s)
16
656
1.80
20
1,024
1.50
24
1,211
1.35
30
1,875
1.20
Hopper^/
3,000
1,200
1.39
Hopper
with overflow
Capacity
(cy)
3,000
without overflow
(if nec.)
600
3.03
Bucke tf*_!
Bucket
5
200
2.50
Size (cy)
15
650
1.60
Suction
-
25-5,000
1.50
Dustpan
-
25-5 ,000
1.50
Mudcat
-
60-150
1.50
Pneuma
-
60-390
1.05-3
Oozes
-
450-650
Clean-Up
-
500-2 ,000
1.23
2/Values shown are representative for Commencement Bay for the cutterhead,
hopper, and bucket dredges. Values for other dredges are derived by relation
to conventional equipment. Variability may exceed + a factor of 2-3.
2/Mobilization costs not included. Price based upon 1-mile transport
distance, 20 feet lift, soft sandy silt material, 1983 pricing, and maximum
single pass excavation depth.
3_/Based upon 35 c.y. per minute pumping, 8 knots average dredge speed,
5 minutes for disposal, silty sand shoaled materials, 80 percent effective
working time, 3 miles distance to disposal site, and cost of dredge operation
at $1,300 per hour.
4/Baaed upon dredging silty sand with disposal site at a 3-mile transport
distance» and 1983 prices.
5-3
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TABLE 5-3
COST OF DISPOSAL AND CONTROL OPTIONS
FOR HANDLING CONTAMINATED SEDIMENTS^/
Alternative Cos tj_/
Disposal:
Site preparation
- upland/near shore $500,000.3/
Weir Construction
- upland $25 ,000
- nearshore $35 ,000
Diking - imported materials $4./c.y.
- onsite materials $l./c.y.
Open-water vertical diffuser
- construction $50 ,000 - $100 ,000
- operation +$1.-2./c.y.
Offsite material transport
- truck +$.20/c.y./mi
- barge +$.20-.25/c.y./mi
Site Control:
Open-water capping material $1.40/c.y.
Liners - soil (volume) $16 .29-18.29/c.y.
- soil (area) $1.81-2.03/ft2
- synthetic $.11-1.50/ft2
Surface covers $1.27-24.20/yd2
Underdrains $2 ,500/ac
Sediment Stabilization
- lime $10,000-14,000/ac
- dust pallatives $1,000-17 ,000/ac
- water sprinkling $2 ,000/ac
_1/Treatment costs not included because of their dependence on flow rates
(see tables 5-7 and 5-8).
2/U.S. dollars, January 1984.
3/Average for potential sites identified in Commencement Bay. Includes
diking and weir costs.
5-4
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TABLE 5-4
DISPOSAL SITE PREPARATION COSTS 1/
Capacity Preparation
(xlOOO c.y.) Dike and Cost per
Weir Costs Cubic Yard ($)
Upland Sites
Puyallup Mitigation 1,000 185 .19
Port of Tacoma "D" 100/1 ,5501/ 62/2751/ .62/. 18
Puyallup River/Railroad 1 ,300/3,3001 505/1,6751// .39/.51
Port of Tacoma "E" 1,700 250 .15
Hylebos Creek Nos. 1 & 2 775/1 ,7751/ 264/1,000l/ .34/.56
Nearshore Sites
Middle Waterway 650 303 .47
Milwaukee Waterway 2,160 925 .43
Blair Waterway Outer Slip 892 788 .88
Blair Waterway Middle Slip 945 412 .44
Blair Waterway Inner Slip 600 341 .57
Blair Graving Dock 200 90 .45
Hylebos Waterway No. 1 1,274 615 .48
Hylebos Waterway No. 2 300 295 .98
J_/Site acquisition costs not included
2/+20 ft MLLW/+35 ft MLLW
5-5
-------
TABLE 5-5
REPRESENTATIVE COSTS FOR SYNTHETIC LINERS
Geotextile Fabrics $.11 - .33/f12
Membrane Liners*
Nonreinforced Materials
30 Mil PVC 0.25 - 0.30/ft2
30 Mil CPE 0.35 - 0.40/ft2
30 Mil Butyl/EPDM 0.45 - 0.50/ft2
30 Mil Neoprene 0.70 - 0.75/ft2
100 Mil HDPE 1.00 - 1.50/ft2
Reinforced Materials
36 Mil Hypalon (CSPER) 0.50 - 0.55/ft2
60 Mil Hypalon (CSPER) 0.80 - 0.90/ft2
36 Mil CPER 0.50 - 0.55/ft2
*Prices from Watersaver, Inc., based upon 400,000 ft2 installations,
5-6
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TABLE 5-6
UNIT COSTS FOR SOIL LINER AND SURFACE COVER MATERIALS
Material and/or Method of Installation
Topsoil (sandy loam), haulingj spreading» and
grading (within 20 miles)
Clay hauling, spreading, and compaction
Sand hauling
spreading and compaction
Cement concrete (4 to 6" layer), mixed, spread
compacted on-site
Bituminuous concrete (4 to 6" layer, including
base layer)
Lime or cement, mixed into 5" cover soil
Bentonite , material only; 2" layer, spread and
compacted
Fly ash and/or sludge, spreading, grading, and
rolling
1982 Unit Costs
$15.73/c.y.
$16.29/c.y.
$18.15/c.y.
$9,690-12,200-acre
$7.26-12.10/yd2
$3.81-6.35/yd2
tl.91-2.67/yd2
$1.78/yd2
$1.27-2.16/c.y.
Source: EPA, 1982.
5-7
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TABLE 5-7
TREATMENT LEVEL COSTS COMPARISON FOR NEARSTIORE SITeJ./
(30 acres)
Cost ($1,000)
Cost
Component
Construction
4-Month
O&M
Unit
Process
Cumulat ive
Total
Dredging 1,000 ,000 c .y .
1 ,500
1 ,500
LEVEL I
Plain Sedimentation
Chemical Clarification
Filtrat ion
Option 1 - Pervious Dike
Option 2 - Sandfill Weir
5 ,880
214
75
86
50
220
5
20
5 ,930
434
80
106
7 ,430
7,864
7 ,944
7 ,970
LEVEL II
Prec ipitation
869
464
1,330
(Assume Option 2
in Level I)
9 ,300
LEVEL III
Carbon Adsorption - Option 1
Ozonation - Option 2
5 ,000
1,600
495
300
5 ,500
1,900
14 ,800
16 ,700*
LEVEL IV
Distillation
Electrodialysis
Reverse Osmosis
Ion Exchange
4 7,850
24 ,850
28,850
21,350
4 ,452
82 7
598
987
52 ,300
25 ,700
29 ,450
22 ,300
(Assume Option 2
in Leve1 III)
69 ,000
42 ,400
4 i , 150
39 ,000
*LEVEL III - Total cost includes Option 1 Carbon Adsorption, plus Option 2 Ozonation.
_l/Costs for site control and treatment at a nearshore site can not be directly compared to costs
for an upland site: treatment levels contain different site control options.
-------
TABLE 5-8
TREATMENT LEVEL COSTS COMPARISON FOR UPLAND SITE±/
(80 acres)
Cost ($1,000)
Cos t
Component
Construction
4-Month
O&M
Unit
Process
Cuinu lat ive
Total
Dredging 1,000,000 c.y.
1,500
1 ,500
LEVEL I
Plain Sedimentation
Chemical Clarification
Filtration
Option 1 - Pervious Dike
Option 2 - Sandfill Weir
15,762
214
75
86
50
220
C
V
20
15 ,812
434
80
106
17 ,312
17,746
17 ,826
17 ,852
LEVEL II
Precipitation
869
464
1,333
(Assume Option 2
in Level I)
19,185
LEVEL III
Carbon Adsorption - Option 1
Ozonation - Option 2
5 ,000
1,600
495
300
5 ,495
1,900
24 ,680
26 ,580*
LEVEL IV
Distillation
Electrodialysis
Reverse Osmosis
Ion Exchange
47 ,850
24 ,850
28,850
21,350
4 ,452
82 7
598
987
52 ,302
25 ,677
29 ,448
22 ,337
(Assume Option 2
in Level III)
78 ,882
52 ,257
56 ,028
48,917
*LEVEL III - Total cost includes Option 1 Carbon Adsorption, plus Option 2 Ozonation.
JL/Costs for site control and treatment at an upland site can not be directly compared to costs for
a nearshore site: treatment levels contain different site control options.
-------
$150,000 and ^200,000 to mobilize and demobilize. Large- to medium-sized
pipeline dredges should only be considered for use on projects where
quantities to be dredged are sufficient to spread mobilization costs.
The operational cost of dredging per c.y. of sediment decreases as pipeline
size increases. Table 5-1 shows dredging costs for typical cutterhead
dredges. Cost for minimum depth pass excavation can be calculated from tables
5-2 and 6-1 as follows:
. ,w. _ s (Maximum Depth Pass Excavation) # _ \
Cost/c.y. (Mm. Pass) = /0 —: —: r x Cost/c.y. (Max. Pass)
J (1/2 x Discharge Diameter)
b. Suction and Dustpan. The cost per c.y. for the suction and dustpan
dredge are comparable to those for cutterhead pipeline dredges shown in table
5-2. Since all dustpan dredges are located on the Mississippi River at this
time, relocation of these dredge types would be an important cost factor.
c. Hopper. Operational costs for hopper dredges range from $700/per hour
to over $2 ,000/per h our. Table 5-2 shows cost and production rates for a
hopper dredge working in a Commencement Bay waterway and disposing at the
existing DNR open-water disposal site. Since hopper dredges are self-propel-
led, mobilization and demobilization costs are usually not a significant
factor in their use.
d. Special-Purpose. Very little information exists on the cost of using
special-purpose dredges, either due to lack of experience or the proprietary
nature of these machines. Typically, these dredges are used in relation to
material requiring some degree of special handling and predisposal treatment.
In these cases, treatment and disposal will represent the bulk of the cost and
be the cost controlling factors, not the dredging. Available cost information
usually does not make the distinction between dredging and treatment costs.
Modifications of conventional equipment, such as the cleanup or refresher
dredges, once installed and without considering developmental maintenance
costs, would move material at a cost proportional to production rate obtained
and comparable to conventional equipment. The pneuma pump, on certain smaller
jobs such as berth cleaning, has been shown to be more cost effective than a
cutterhead dredge.
5.02.03 Mechanical Dredges. The bucket dredge typically operates at speeds
of 30 to 60 buckets per hour. Larger buckets generally resuspend less mate-
rial per c.y. removed and are more cost effective. Because of this, only
medium and large bucket sizes were considered for possible use in Commencement
Bay. Table 5-2 compares cost, production rates and dredging depths for medium
and large bucket dredges. These dredges are abundantly available in the
Pacific Northwest; consequently mobilization costs are not a significant cost
factor.
5.03. Disposal Costs.
5.03.01. General Cost Principles. This section describes general principles
affecting sediment disposal costs and estimates expenses of implementing dis-
posal at the various pontential sites in and around Commencement Bay. In our
5-10
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evaluation of disposal costs, a number of factors were considered, including
site preparation, transportation, and other costs associated with initial or
ongoing disposal of sediment. The portion of disposal costs related to trans-
porting the dredged material to a disposal site and discharging and distri-
buting it within the site is included in the costs presented for dredging.
Transportation costs addressed in this section relate to modified control of a
discharge (e.g., vertical diffusers) and control of return effluent (e.g.,
we ir).
The selected disposal method will have less influence on cost than will the
selected particular disposal site, i.e., the key to cost evaluation of
disposal is not necessarily the method (open-water, nearshore, or upland), but
the location of the particular disposal site and the site preparation needs it
might require. Open-water disposal, for which there are normally no
acquisition costs, may have a total cost comparable to the other methods due
to site preparation costs (if needed), capping volumes necessary (resulting in
increased dredging volumes and, hence, total cost), and the greater difficulty
in monitoring. Site preparation costs for the other two methods are roughly
similar (about $500,000 average in Commencement Bay), although they can vary
widely based on specific site conditions. Table 5-3 summarizes costs for the
disposal options evaluated.
5.03.02. Open-water Disposal. Open-water disposal costs are normally
relatively low for uncontaminated materials. For contaminated material, costs
will increase depending upon the selected methods of site preparation and
material placement, and upon measures taken to control contaminant release,
such as capping and cap thickness. The use of an underwater diffuser
increases open- water disposal cost. A construction or acquisition cost of
the underwater diffuser is estimated at between $50,000 and $100,000; however,
no commercial firms are manufacturing diffusers at this time. A crane and
barge would be required to operate the diffuser at the depths required for
disposal in Commencement Bay, and this would increase disposal costs by an
additional $.50 per c.y. to $.75 per c.y. If materials from a barge or hopper
dredge were reslurried and pumped through the diffuser, cost would increase an
additional $.75 to $1.25 per c.y. For smaller or one-time dredging projects,
it is roughly estimated that the use of the diffuser would increase the
disposal cost of cutterhead pipeline dredged materials $1 per c.y. and
increase the cost of hopper dredged or clamshell dredged material over $2 per
c.y. For larger projects, these costs can be expected to drop.
The costs of capping contaminated material discharged at an open-water dis-
posal site will either be an additional cost (if the cap material is being
dredged solely to provide a source of cap material) or part of the overall
dredging cost (if the cap material is part of the required dredging).
a. Deep-water Mound. Unconfined mounding of contaminated sediments
generates a relatively large surface area to be covered. Assuming disposal of
100,000 c.y. of contaminated material, it is estimated that the cap volume to
provide 3 feet of cover would range between three and five times the disposal
volume. A volume of four times was selected (400,000 c.y.) to be placed by
5-11
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hopper dredge bottom dump. With a cost of capping material (dredging, trans-
port, and discharge) estimated at $1.50 per c.y., the total cost for this cap
would be $600,000.
b. Deep-water Confined. Confining the contaminated material by burial
in a depression (possibly with partial underwater diking) results in less sur-
face area requiring cover and allows the use of a vertical pipeline diffuser.
For the same 100,000 c.y. disposal, only an additional 100,000 c.y. of clean
material was assumed to provide adequate cover. Use of a cutterhead pipeline
dredge at a base cost of $1.50 per c.y., and adding to this the increased cost
of the diffuser system at $1 per c.y., capping costs would be $250,000. Use
of a vertical pipe allows construction of underwater diking at a cost compara-
ble to capping (about $2.50 per c.y.). Diking may totally encircle the site
or be in combination with existing natural features (e.g., rock outcrop).
This design is more expensive than deep-water mounding due to site preparation
but may be easier to cap.
5.03.03 Upland Disposal. Cost of upland disposal will vary according to
specific site characteristics. Factors include ownership of the site, amount
of site preparation necessary, distance from the dredge site (may include
transportation method), and, for the disposal of contaminated materials, the
amount of treatment and monitoring required both during and after disposal and
capping. For Commencement Bay, weir construction is estimated at about
$25,000. Upland sites in Commencement Bay that are in the elevation range of
+8 to +12 MLLW may require that all diking materials be trucked to the site.
At this elevation, the water table is near the surface and existing native
soils may not be sufficient or suitable for dike materials. Granular fill
adequate for diking materials is available from the gravel pits on the bluff
north of the Hylebos Waterway. The estimated cost of importing materials and
dike construction is $4 per c.y.
Where existing ground elevation is higher because of previous fills, the
existing surface material may be utilized for diking. Use of existing mate-
rials would reduce the cost of diking to approximately $1 per c.y. While
coarser fill materials are easier to use for diking, finer soils that can be
included in diking will reduce leakage of effluent water through the dike. An
associated cost, though one not included in our analyses, involves the ulti-
mate use of the land filled. If disposal can be designed to ultimately allow
development to occur, at least some of the initial costs of disposal may be
recoverable. This is not possible for open-water disposal.
5.03.04 Nearshore Disposal. The cost factors for confined disposal sites are
described under upland disposal. Costs for nearshore disposal site prepara-
tion are normally higher than for upland as an adequate foundation for dikes
and the weir must be provided. For the weir alone, additional cost was esti-
mated at about $10,000 for a total estimate of $35,000. The primary cost
advantage of nearshore disposal over open-water or upland disposal is that
nearshore sites are normally located close to the dredging site(s), saving
transportation costs. Additionally, most nearshore sites are ultimately
planned to be developed so some cost recovery can be anticipated.
5-12
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5.03.05 Off-site Disposal. The differences between local and off-site dis-
posal involve increased costs for transportation of the contaminated materials
to the offsite disposal area and the problems of retaining the contaminants
during that transport. The latter problem can be effectively handled by
current technologies associated with transportation of hazardous materials; it
is, however, expensive. The increased costs would depend upon the transporta-
tion mode selected and associated controls and treatments required. Barging
of dredged material to an open-water site outside of the Commencement Bay area
was considered initially, but was dropped because no likely specific site
could be identified based on existing information. Estimated transportation
costs for barging would be an addition of approximately $.20 to $.25 per c.y.
per mile. Transportation costs for trucking dredged material (but not
including dewatering or rehandling charges) was estimated at an additional
$.20 per c.y. per mile.
5.03.06 Potential Disposal Site Costs. The following section addresses site
preparation costs for the potential disposal sites identified in Commencement
Bay. In all cases, site acquisition costs were not investigated. Table 5-4
summarizes disposal site preparation costs.
a. Puyallup River Delta Site. There may be expenses involved in having
DNR redesignate the site for open-water disposal. The site is located within
2 miles of most anticipated dredging sites; therefore, transport of dredged
material would be minimal. The site's slope could make capping difficult and
might necessitate some site preparation in order to confine contaminated
sediments.
b. Department of Natural Resources Site. The location of this open-water
site places it beyond the most economical pumping distance for pipeline
dredges (a booster pump would be necessary). Use of a vertical pipeline
diffuser is possible with commensurate cost increase ($1 to $2 per c.y.). If
underwater dikes are constructed, a vertical pipeline diffuser would be
necessary.
c. Hylebos/Browns Point Site. There may be expenses involved in getting
the site designated by DNR as an open-water site due to lack of information
about the area. The site is within economical pumping and haul distance for
all dredges. Use of a vertical pipeline diffuser is possible ($1 to $2 addi-
tional per c.y.) and would be required to construct the underwater dike.
d. Puyallup Mitigation Site. This upland site is located within reason-
able economical pumping and haul distance. Existing fill material can be
utilized for dike construction at a cost of about $1 per c.y. Estimated diking
cost is $160,000 and weir construction is $25,000 for a total preparation
estimate of $185,000.
e. Port of Tacoma Site "D". This upland site is well within economic
pumping and haul from most potential dredging sites. As existing fill could
be used for dike construction. Dike and weir construction for fill to +20
feet MLLW is estimated at $62,000. The same cost to fill to +35 feet MLLW is
$275,000.
5-13
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f. Puyallup River/Railroad Site. This upland site would probably have t
be purchased from the owner and the claim by the Puyallup Tribe resolved.
Diking and weir costs to fill the site to +20 feet MLLW were estimated at
$505,000. The same cost to fill to +35 feet MLLW would be $1,675,000. Given
the site location, use of a booster pump for hydraulic dredge disposal may be
necessary for some dredging sites.
g» Port of Tacoma Site "E". This upland site is within economical pump-
ing and haul distance from Blair, Sitcum, and Hylebos Waterways. Existing
fill material could be used in dike construction; diking and weir costs were
estimated at $250,000.
h. Hylebos Creek Sites Nos. 1 and 2. These two upland sites would
probably have to be acquired from their owners. The sites are within the
economic pumping and hauling distance. Diking and weir construction for fill
to +20 feet MLLW was estimated at $264,000 and to +35 feet MLLW at $1,000,000
i. Middle Waterway Site. Relocation or compensation to waterway users
may be required for this nearshore site. It could receive dredged material
from anywhere in the harbor economically. Site preparation costs are esti-
mated to total $303 ,000 , including $240,000 for dike construction, $28,000 fo
slope protection (riprap), and $35,000 for the weir.
j. Milwaukee Waterway Site. Dredged material from anywhere in
Commencement Bay could be disposed of economically at this nearshore site.
Total site preparation cost was estimated at $925,000, including $716,000 for
diking, $174,000 for slope protection, and $35,000 for weir construction.
k. Blair Waterway Slips. All of these nearshore slips could accept
dredged material from anywhere in Commencement Bay. Site preparation costs
for the outer slip were estimated at $788,000, including $678,000 for diking,
$75,000 for slope protection, and $35,000 for weir. Site preparation costs
for the middle slip were estimated at $412,000, including $339,000 for diking
$38,000 for slope protection, and $35,000 for the weir. Site preparation
costs for the inner slip were estimated at $341,000, including $265,000 for
diking, $41,000 for slope protection, and $35,000 for the weir.
1. Blair Graving Dock Site. Preparation costs for this nearshore site
were estimated at $90,000, including $50,000 for diking, $15,000 for slope
protection, and $35,000 for the weir.
m. Hylebos Waterway No. 1. Preparation costs for this nearshore site
were estimated at $615,000, including $480,000 for diking, $100,000 for slope
protection, and $35,000 for the weir.
n. Hylebos Waterway No. 2. Total preparation costs for this nearshore
site are $295»000, including $200,000 for diking, $60»000 for slope protec-
tion, and $35,000 for the weir.
5-14
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5.04 Control and Treatment Costs.
5.04.01 Control and Treatment Cost Principles. Costs for control features
discussed in chapter 4 are summarized below. However, costs for treatment
processes are highly dependent on flow rates to be treated. Flow rates will
vary depending on the size and type of dredge, the type of site water, and
flow rate controls that are available. Therefore, costs of treatment unit
processes are not provided in this chapter. Instead, costs are provided for
application of these processes to example disposal areas as a way of illus-
trating relative costs. Site control and treatment measures are combined into
these example designs.
Table 5-5 shows the range of synthetic liner costs in upland disposal areas.
Representative costs for soil liner and surface cover materials are shown on
table 5-6. Placement of a soil liner under water in a nearshore site could
increase costs by $1 to $2 per c.y. An underdrainage system for an upland
site is estimated to cost $2 ,500/acre.
There is a limited amount of cost data available for sediment stabilization
methods. The following are estimates of cost for the various methods:
o Lime mixed into 5 inches of cover soil would cost from $10,000 to
$14,000 per acre.
o Agronomic methods to control dust pallatives include revegetation of
the site. Capital costs include area preparation, seeding, fertilizing, and
mulching. These costs would be about $1,100 per acre. Operation and mainte-
nance costs would include grass mowing and re fertilization.
o The cost for a sprayed asphalt membrane is about $10,000 to $17,000 per
acre.
o Soil cement stabilization costs about $15,000 per acre,
o Costs are not readily available for biological decontamination methods,
o Water sprinkling systems cost about $2,000 per acre.
5.04.02 Nearshore vs. Upland Treatment Costs. The following discussion is
not intended to represent actual costs for specific sites, but is intended to
illustrate the different factors affecting costs for nearshore and upland
disposal areas. Several simplifying assumptions are made for costing the two
site alternatives. Among these are:
o project size equals 1,000,000 cubic yards;
o upland site is 80 acres",
o nearshore site is 30 acres;
5-15
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o 24-inch hydraulic pipeline dredge operating 10 hours per day for
4 months;
o site control required for upland site includes covers, liners, and
underdrains (leachate collection);
o site control for the nearshore site includes only a soil liner and
cover;
o levels of treatment are applied only to effluent during disposal
operations, and to runoff and leachate treatment;
o levels are additive for costing purposes; and
o postclosure facility monitoring and maintenance costs are not included.
Costs are current to January 1984 price levels- Pricing information which was
obtained from published reports and technical manuals has been updated to
current levels based on Engineering News Record (ENR) construction cost
escalation factors. Cost of salvage was assumed to equal cost of demolition
at project completion. Contingencies represent allowances for unforeseen
conditions and factors not known at this level of investigation. A larger
contingency factor was applied to nearshore plain sedimentation than to upland
plain sedimentation because of the greater potential for unknown costs
associated with work below the water table. Operation and maintenance costs
include the estimated cost for labor, chemicals, testing, and energy require-
ments for the particular alternative.
While cost of treatment systems can be compared within each of the representa-
tive sites, it must be emphasized here that cost comparisons between sites is
not possible for several reasons. First, costs are based on placing the same
quantity of dredged material in sites of different capacity. Discharging
additional material into the larger site would reduce the cost of treatment
per c.y. of material discharged. Second, costs for treatment at the upland
site include several treatment methods that cannot be implemented at the near-
shore site without site dewatering. Dewatering would require extraordinary
and extremely expensive construction techniques and is, therefore, not con-
sidered here. Third, foundation material in the nearshore zone may not he
adequate to support the necessary diking. Seismic potential, mud foundations,
and tidal fluctuations can threaten dike stability. As a result, construction
in the nearshore zone has a higher risk of failure. Fourth, equivalent treat-
ment in each site would produce lower containment of contaminants in the
nearshore site due to the factors operating on contaminant mobility and the
limited site control relative to upland sites.
Costs based on the above assumptions are summarized below. Detailed cost
tables and supporting calculations used to develop treatment level costs are
found in appendix 3.
5-16
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o The costs for site control and treatment in the nearshore site evalu-
ation example are shown in table 5-7. The costs range from $7,970,000
(Level I) to $69,000,000 (Level IV).
o Upland disposal area site control and treatment costs are summarized in
table 5-8. The costs range from $17,852,000 (Level I) to a maximum of
$78,882,000 (Level IV).
The cost of plain sedimentation represents the majority of treatment costs
compared to chemical clarification, filtration, and metals precipitation. The
addition of these latter treatment methods may be'relatively cost effective
measures of obtaining substantial additional contaminant removal. For organic
contaminants, Level III treatment provides high removal efficiency at a cost
increase of 40 (upland) to 80 (nearshore) percent. Level IV treatment of the
site effluent would be unlikely for several reasons. First, organic contami-
nants are a major part of the sediment contamination in Commencement Bay and
Level III treatment is highly effective for organic contaminant removal.
Second, Level IV treatment of the high rate effluent flow represents a sub-
stantial additional cost. Third, Level IV treatment processes have not been
well documented for high rate application to multiple-contaminant slurries.
As a result, Level IV treatment is only a likely consideration for site runoff
and leachate , where the alternative of using an existing municipal or indus-
trial facility may be available. Of the Level IV treatment systems, distil-
lation is the most expensive, best documented, and best performing process
available.
5.05 Other Cost Factors. Since many of the cost estimates provided in this
report are based on illustrative examples, the sensitivity of costs to
quantity of material being dredged and degree of contamination is briefly
discussed here. The key to the effect of job size on cost is the mobiliza-
tion, construction or other "up-front" costs. These costs are spread out over
the quantity of material handled. For dredging, the mobilization of a large
dredge can add 7.5^/c.y. on a large dredging job (2 million c.y.), but can
easily add up to $1.50/c.y. for a small job (100,000 c.y.). For disposal,
spreading the costs of diking, weir construction, and land acquisition/
development is much the same idea as for dredging. With control and treat-
ment, the flow rate will have a major effect on costs, but the substantial
construction costs of many of the treatment facilities can be spread out over
increased quantities. In conclusion, there are strong economic incentives to
centralize disposal and treatment facilities and maximize their use.
Commencement Bay contamination is predominantly "low saturation" in the
chemical sense, that is, sediment contaminant concentrations are mostly less
than 50,000 ppm in sediments. Once it is determined that a treatment or
control is needed (i.e., criteria are exceeded), treatment measures can be
expected to be equally as effective with twice the contaminant concentration
as with half the concentration observed in the sediments. The cost of treat-
ment is, therefore, relatively independent of contaminant concentration, once
criteria have been exceeded.
5-17
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CHAPTER 6.0 DISCUSSION AND CONCLUSIONS
6.01 Introduction. Previous chapters provide a description and evaluation of
alternative dredging, disposal, site control, and treatment methods and their
costs for use with contaminated sediments. This chapter compares and dis-
cusses these methods, presenting those conclusions that can be formulated at
this stage of planning for Commencement Bay. First, preferred dredging
methods and possible tradeoffs for various types of sediment contamination are
addressed. Disposal methods are ranked in terms of the major factors that
would influence decisions on disposal of contaminated sediments. Likely
application of contaminant treatment techniques in Commencement Bay is
presented. Second, the relative contaminant loss or confinement obtained
during each stage of the handling process (dredging, disposal, control, and
treatment) is discussed. Third, disposal sites are evaluated and recommenda-
tions on preferred or most appropriate sites for near-term consideration are
presented. Fourth, information needs and data gaps for handling of contami-
nated sediments are identified. Research or tests that merit priority
consideration at this time are discussed.
6.02 Dredging Methods.
6.02.01 General. Operating characteristics of hydraulic and mechanical
dredges are summarized in table 6-1. Cost and resuspension values, while
representative to the extent that they fall within normal ranges for a given
dredge, are derived from various sources with unique conditions. Therefore,
these values have not been normalized and comparisons between dredging methods
must acknowledge their variability. In terms of sediment resuspension at the
dredge site, this table illustrates that .special-purpose hydraulic dredges
produce less resuspension than conventional hydraulic dredges, and, with the
exception of hopper dredge overflow, conventional hydraulic dredges produce
less resuspension than mechanical dredges.
In terms of slurry water that may require treatment at the disposal site,
mechanical dredges do not produce a slurry, conventional hydraulic dredges
produce abundant slurry water, and special-purpose dredges fall somewhere in
between. In terms of cost, dredges are for the most part comparably priced.
However, job specific factors can produce substantial cost differences between
dredge types. Many of the dredges listed in the table are readily available
for use in Commencement Bay. The notable exception is the group of special-
purpose dredges for which availability could be a major cost factor to be
considered.
Until recently, many of the special-purpose dredges have had lower production
rates than conventional equipment. This is still true for several of these
dredges, but newer equipment such as the refresher and oozer appear to have
production rates comparable to conventional hydraulic dredges. For barge or
hopper-hauled dredged materials, production will vary depending on proximity
of the disposal site, but it is usually less than what can be obtained by a
continuously operating cutterhead dredge.
6-1
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TABLE 6-1
SUMMARY OF DREDGE OPERATING CHARACTERISTICS
Percent Solids
Sed iment
Approximate
in Slurry or
Resuspension Above
Range of
Vert ica1
Horizontal
Transported
Background
(mg/l)b
Product ion
Dredging
Depths
Dredging
Dredging
Material
near
near
Rates
(ft)
Accuracy
Accuracy
by Weight®
bottom
surface
(c.y. yd/hr)
Minimum
Maximum
c± ft)
(± ft)
Availab ility
Bucket
up to 100%
106
134
30-600
0d
150e
2
1
Pacific Coast
Suction
10-15Z
—
—
25-5,000
5-6
50-60f
1
2-3
Pacific Coast
Dustpan
10-20?
—
—
25-5,000
5-14
50-60 ^
]
2-3
Mississippi River
Cutterhead
10-20Z
35
134
25-5,000
3-14
12-65f
1
2-3
Pacific Coast
Hopper
10-20Z
2728
627
500-2,000
10-28
65f
2
10
Pacific Coast
Hudcat
10-40Z
145
500
60-150
1]
15
)
!
Pacific Coast
Pneuma
up to 80Z.
4
23
60-390
0d
150e
1
1
Chicago, Illinois
Oozer
up to 80X
0
—
450-650
-
100-150
1
2-3
Japan
Clean-Up
30—402
2 .6
4
500-2 ,000
5-10
60
1
2-3
Japan
Refresher
30-40Z
"
13.5
200-1,300
20
60
1
2-3
Japan
NOTES:
a - Percent solids shown are normal working ranges.
b — Resuspension values shown are considered representative. However, very wide ranges are reported.
c - Cost values shown are representative of Commencement Bay for the cutterhead, bucket, and hopper dredges. Values for other dredges are derived bv
relation to conventional equipment. Variability may exceed + a factor of 2-3.
d - Zero if used alongside of waterway; otherwise, draft of vessel will determine,
e - Demonstrated depth; theoretically could be used much deeper.
f - With submerged dredge pumps, dredging depths have been increased to 100 ft or more,
g - Value shown is average at 3 feet below surface.
-------
Hydraulic dredges produce less solids resuspension at the dredging site and
have a higher removal efficiency for liquid and solid phases than do mechani-
cal dredges. Hydraulic dredges with passive heads (e.g., suction, pneuma,
etc.) and shrouded heads (e.g., refreshers, mudcat, etc.) produce less
resuspension than do exposed, active heads (e.g., cutterhead). However, use
of a hydraulic dredge to obtain high removal efficiency at the dredging site
involves a tradeoff requiring consideration of slurry water and sediment
consolidaton at the disposal site.
Different dredging methods appear more appropriate for certain contaminant
classes. For loss of volatile contaminants during dredging, mechanical
dredges will likely perform better than hydraulic dredges. For sediment-bound
contaminants, greater removal is obtained by hydraulic dredges than by
mechanical dredges and appropriate technology exists for control of solids at
the disposal end. Soluble contaminants can be removed more efficiently by a
hydraulic dredge, but are difficult to control at the disposal end and treat-
ment of the effluent water may be required.
Most projects are likely to contain all three types of contamination, con-
founding a decision on appropriate dredging technique. In terms of overall
contamination, sediment-bound contaminants usually represent the bulk of the
contamination, suggesting use of hydraulic equipment for maximum recovery and
extraction efficiency. The amount of volatiles that may be lost during
dredging are not likely to be a source of major concern in many projects.
Therefore, as the types and amount of soluble, or easily solubilized, con-
taminants increase in a sediment to be dredged, greater consideration should
be given to the relative cost and environmental impact of mechanical dredging
with watertight equipment to that of hydraulic dredging and water treatment at
the disposal site. This evaluation is likely to be the key to selecting a
dredge for a given contaminated sediment.
A variety of equipment modifications are appropriate for dredging contaminated
sediments. Many of the practices that increase production of a hydraulic
dredge will also reduce sediment resuspension and contaminant loss. The
walking spud and ladder pump are prime examples; however, their availability
is a function of the original dredge design, which may limit their use in
Commencement Bay. Production meters installed in the pipe will contribute to
reduced resuspension and are readily available and adaptable to existing
equipment. Use of large, watertight buckets will substantially reduce sedi-
ment resuspension and loss of interstitial water during mechanical dredging.
Operational modifications to be considered for hydraulic cutterhead dredges
include minimizing cutter revolution speed, controlling swing speed, and not
overdigging the maximum cut depth. Additional research is ongoing to quantify
the effect of these practices. The problem of limiting the environmental
impact of dredging contaminated sediments through reducing resuspension of
sediments is being addressed by the WES of the Corps of Engineers under a
research program known as the Improvement of Operation and Maintenance
Techniques (IOMT) program. For hopper dredges, operating in sandy silts or
silty sands without overflow can have a significant impact on cost. There-
fore, it may not be practical to use a hopper dredge for projects with high
6-3
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concentrations of ^oluble contaminants. For mechanical dredging, sweeping the
bottom with the bucket and digging fine-grained sediments from underneath
(heavy buckets penetrating through soft surface materials) are practices to be
avoided in contaminated areas. For most operator controls or operational
modifications, serious consideration should be given to hourly rental of
dredging equipment rather than bidding in order to maintain control of project
costs and better define cost factors during first-time use of modifications.
6.02.02 Selection of a Dredge Type. Short-term losses of soluble contami-
nants represent the key in selecting dredge type. These losses can be esti-
mated by assuming a slow rate of contaminant transfer between phases during
dredging and using a modified elutriate test. For hydraulic dredging, test
results are used to predict weir concentrations (total and dissolved) expected
for a given site. Predicted values can be compared against dec isionniak ing
criteria with or without consideration of dilution in the receiving waters.
It is more difficult to predict losses for mechanical dredging. Bucket size,
sediment characteristics and other job-specific factors will influence the
actual losses in the field. As a usual rule, within the options that are
generally considered for large-volume, low-level contaminated sediments dredg-
ing, hydraulic dredging with particulates control will likely provide greater
confinement per given cost than will mechanical with watertight equipment for
situations where a low percentage of the contamination is soluble. As the
percentage of soluble contaminants increases, the "confinement-per-cost"
indicator will begin to favor the mechanical approach.
However, when considering high-level contaminated sediments, the greater
extraction and transport efficiency of hydraulic dredging is an important
factor. Overall, the technology for addressing contaminated sediments is
better known for hydraulic dredges than for mechanical dredges.
Selection of a dredge requires consideration of all the factors mentioned in
paragraph 2.01 and of the disposal and treatment options available. Several
dredges may be able to meet criteria by employing one or many of the available
dredging techniques. Therefore, identification of the criteria that are to be
met is the first and most important task in selecting appropriate equipment.
6.03 Disposal Methods. Evaluation of disposal methods with the idea of
defining the appropriate and most efficient means of confining contaminants in
the long term is difficult. Contaminants gradually will move back into the
environment from wherever they are placed. The factors that influence the
speed with which they will release from the disposal site are the mobility of
the contaminant* the phase with which the contaminant has associated itself in
the sediment (gas, liquid, solid), and the physical/chemical environment into
which the contaminant has been placed. Given that most projects will contain
more than one class of contaminants, the evaluation becomes complex and
variable.
The key considerations involved with disposal method effectiveness are:
o the class of contaminants of concern,
6-4
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o the similarity of the disposal site conditions to in situ conditions,
and
o the number and magnitude of transport mechanisms operating at the
disposal site.
Two final considerations acknowledge the impossibility of permanent con-
taminant retention:
o the degree of control or treatment possible to intercept migrating
contaminant fractions, and
o the risk of significant adverse effects from contaminants released by
the disposal method.
Table 6-2 provides the major evaluative factors pertinent to disposal
methodology and rates the three general disposal methods against those factors.
It is important to know what classes of contaminants are associated with the
sediment, what phase the contaminants are associated with in the sediments,
and how they are partitioned between phases in situ in order to predict long-
term mobility. In general, leaving, or disposing of, contaminated sediments
TABLE 6-2
COMPARISON OF DISPOSAL METHOD EFFECTIVENESS
Geochemical
Magnitude of
Available
Environmental
Effect on
Contaminant
Control/
Risks From
Disposal
Contaminant
Transport
Treatment
Contaminant
Me thod
Mobilization
Mechanisms
Options
Release
Open-Water,
Low
Diffusion: High
Few
Low due to
capped
Convection: Medium
dilution
Bioturbation: Varies
(Resource
Erosion: Medium
risk)
Upland,
High
Diffusion: Low
Many
Varies by
confined
Convection: Low
contaminant
Volatilization: High
(Human health
Bioturbation: Varies
risk)
Erosion: Low
Nearshore,
High in
Diffusion: High
Some
Medium
confined
Unsaturated
Convection: High
(Human
Zone; Medium
Volatilization: High
health &
in Saturated
Bioturbation: Varies
resource
Zone
Erosion: Low
risks)
6-5
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in a chemical environment as close as possible to their in situ state favors
contaminant retention (especially metals). However, placing the sediments
into different, or into shifting, physical or chemical environments (upland
and nearshore) will encourage some contaminants to move between phases.
Geochemical changes associated with air and oxygen in these disposal sites can
change sediment pH (mobilizing metals) and alter sediment organic carbon
(mobilizing organics). For organic contaminants, the influence of these
geochemical changes on contaminant mobility may be outweighed by the effect of
water exchange occurring at the site. It is also important to note that while
contaminant mobility and release can serve to define disposal method effec-
tiveness, release of contaminants will have different environmental effects in
different disposal sites (i.e., greater mobility at one site may be less
damaging than lesser mobility at another site).
Transport mechanisms have been identified and explained in chapter 3 for the
several disposal methods and designs. Open-water sites, especially those in
deep water, have fewer mechanisms (air is absent) than upland sites. Near-
shore sites have the most transport routes available and are located in a very
active environment; therefore, nearshore disposal is the least preferred
method from a contaminant confinement point of view.
In general, contaminants bound tightly to sediments are the easiest to handle
and contain. Disposal method considerations involve maximizing containment of
solids within the disposal site. Upland and nearshore disposal offers the
greatest potential for retaining dredged material, whether hydraulically or
mechanically dredged. Open-water disposal, because of depth and currents,
allows some fraction of the material placed to escape. Since the material
that would normally escape is fine-grained, and more typically associated with
chemical contaminants, open-water disposal is less efficient at accepting
discharges of contaminated sediments. There are other considerations, how-
ever. Aerobic and unsaturated conditions favor release of heavy metals from
sediment surfaces into solution. Sediments placed in upland and in the
unsaturated nearshore disposal sites would be subjected to chemical stresses
(oxidation, pH decrease, activation of other compounds) due to the less stable
(in the long term) environment. Contaminant fractions would release as gas or
into solution and migrate along seeps or leach into ground water. For heavy
metals* disposal in open-water eliminates the conditions favoring release and
aids retention. However, contaminated sediments rarely contain only heavy
metals. Though many of the organic contaminants found in Commencement Bay are
relatively hydrophobic and have high sorption coefficients, there is no known
way to keep organics bound to the sediment, and all are somewhat soluble.
Placing these compounds in saturated conditions with high water exchange
greatly favors contaminant mobility. In these terms, the nearshore has
greater water exchange than the upland, and upland has greater exchange than
open water.
Volatile contaminant fractions may be lost during dredging or be released only
under unsaturated conditions. The key to the mobility of volatiles is the
surface area and time exposed to air. Material that has been hydraulically
dredged will probably have lost all in situ gases by the time it is placed in
the disposal site. Slurry placed into an open-water site may still contain a
small percentage of entrained gases that will release until the site is
6-6
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capped; mechanicalLy dredged material will still retain most of its in situ
gases. Once capped, the stable, saturated conditions underwater will result
in losses of volatiles about an order of magnitude less than the other
disposal methods due to less air exchange. Sediments placed in upland
disposal sites will drain and volatilization will occur. Disposal in
nearshore environment will result in greater release from the unsaturated
layer than the saturated layer. Mechanically dredged materials that require
rehandling (for transport to or within the disposal site) will tend to lose
volatiles more readily than slurried sediments or than sediments that are not
rehandled. Over longer periods of time, in situ gases will likely build up in
the sediments and provide a mechanism for loss of volatiles. However, the
amount of volatiles lost is not likely to be a source of major concern for
most projects.
Soluble contaminants, or contaminants with the greatest potential to go into
solution under certain conditions, are of more concern because these are less
readily contained. Soluble contaminants in situ at the time of disposal will
be lost if hydraulically discharged in open water, or may require treatment as
effluent from upland or nearshore confined sites. In the effluent, these
contaminants will have been diluted by the volume of new water slurried.
Mechanically dredged sediments will have retained more of their interstitial
water and there will be less quantity to treat; although contaminant con-
centrations will be higher. In the longer term, contaminated sediments placed
in open water will lose their soluble fraction to diffusion and convection;
although this release will be gradual due to the reduced magnitude of trans-
port mechanisms. Materials placed in upland disposal sites also will tend to
release their soluble fractions over time. Due to the more active physical
processes (precipitation, ground water infiltration, etc.) and the unstable
chemical environment, this release will be more rapid than in open-water;
however, it also will be more concentrated and easily intercepted. The near-
shore environment is the most active, having all of the transports of the
uplands and the addition of much more active water exchange than in the open
water due to tidal activity.
Therefore, in terms of contaminant retention, disposal method selection is
more a matter of controlled release than total confinement. Control of the
releases and/or concern with the effects of the release must be considered.
Open-water disposal allows for very limited control of releases other than cap
or liner thickness. This retards contaminant mobility and encourages a con-
stant, gradual release to the overlying water body once the cap has been
saturated by the migrating contaminants. The levels of contaminant concentra-
tion released will be low and will be diluted by the overlying water. The
risk of significant damage in this environment is low and would not likely
affect human health. Upland disposal, on the other hand, allows for the
greatest control, through design considerations, monitoring capabilities,
backup contaminant intercept systems, and treatment facilities. Environmental
risks incurred may be higher than in open-water because of potential human
health concerns. The nearshore disposal option does allow for some greater
control of contaminants than in open water, but many fewer than are available
in an upland situation. In addition, the risks to the environment and to
human health are much greater than in open water, and in most situations, are
6-7
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greater than at an upland site. Looking ahead to development of criteria for
appropriate disposal methods, the interplay of site control and contaminant
mobility suggests, as a generalization, that nearshore sites should receive
the low-level contamination, open-water sites the low-to-medium level con-
tamination, and upland sites the high-level contamination.
6.04 Site Control and Treatment Methods. The applicability and potential use
of various control and treatment alternatives for contaminated sediments in
Commencement Bay are shown in table 6-3. This table illustrates that in going
from upland to nearshore to open-water disposal, the degree of site control
and the number of available treatment options decreases. This decreasing
control is translated into reduced opportunities to design additional treat-
ment measures that would prevent sudden or accelerated contaminant release
into the environment and/or to avoid the extreme expense of sediment removal
and relocation.
As with dredging and disposal, criteria must be known before treatment recom-
mendations can be made. It is logical to assume that disposal of contaminated
material in any area without proper treatment and control could result in
rapid return of the contaminants to the environment. However, the simple
removal of the contaminated sediment from its present location to a new loca-
tion may produce sufficient increased isolation from, or reduced contaminant
loss to, the environment to obtain a net beneficial result. (Note that the
exact opposite is also possible.) But from the management perspective that a
rapid loss of contaminant "in hand" (dredged out of the aquatic system)
represents a lost opportunity at best and an eventual return to existing
deteriorated conditions at worst, the uncontrolled and untreated loss may not
be acceptable. As environmental criteria require more isolation, greater
confinement and less/slower return, treatments exist that can be added to
achieve these standards. Federal and state regulations also provide technical
guidelines for design of site controls and monitoring of site containment
(e.g., State of Washington proposed solid waste regulations). These guide-
lines should be reviewed prior to selection of appropriate site design.
Presuming that eventual criteria require placing only low-level contamination
in nearshore sites, up to medium-level contamination in open-water sites, and
the high-level contamination in upland sites, certain implications to treat-
ment levels are foreseen. All control and treatment options labelled as
"likely" for potential use (table 6-3) are foreseen as being necessary for
respective upland, nearshore, or open-water sites. In addition, as contamina-
tion levels approach the higher range of those allowed for each disposal
method, options such as cap bioturbation monitoring (for open water), carbon
adsorption treatment (for nearshore) and dissolved solids removal from leach-
ate and runoff (for upland) become more probable. These practices should
result in contaminant confinement and removal that is acceptable and meets
criteria in most cases.
6.05 Relative Containment During Dredging, Disposal, Control, and Treatment.
Loss of contaminants during handling of contaminated sediments will occur from
all of the three phases of the sediment with which contaminants are associ-
ated: solids (sediment), water, and gas. These losses can occur during
dredging and disposal, and in the short and long term. For the majority of
6-8
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TABLE 6-3
APPLICABILITY AND POTENTIAL USE OF VARIOUS CONTROL AND TREATMENT
ALTERNATIVES FOR CONTAMINATED SEDIMENTS IN
COMMENCEMENT BAY (NA = Not Applicable)
Disposal Method
: Upland Dis
posal
Nearshore
Disposal
Open-Water Disposal
Potential Use:
Likely
Less Likely
Likely
Less Likely
Likely
Less Likely
Liners
synthetic,
soil
soil
NA
NA
Drains
leachate
drains
NA
NA
NA
NA
Capping
synthetic ,
soil
synthetic,
soil
sediment
Sediment
Stabilization
liming,
pallatives
sprinkling
liming,
pallatives
sprinkling
NA
NA
Suspended
Solids
Remova1
sedimentation,
clarification,
filtration
sedimentation
clarification
fiItration
9
9
NA
NA
Removal of
Solubles
precipitation,
adsorption
ozonation
precipitation
adsorption,
ozonation
NA
NA
Dissolved
Solids
Removal
distillation,
RO, ED, IE
distillation,
RO, ED, IE
NA
NA
-------
TABLE 6-3 (con.)
Disposal Method
: Upland
Disposa1
Nearshore
Disposal
Open-Water
¦ Disposal
Potential Use:
Likely
Less Likely
Likely
Less Likely
Likely
Less Likely
Volatiles
stripping
stripping
NA
NA
Biological
Control
fenc ing ,
sediment
cover
bioc ides
fenc ing,
sediment
cover
biocides
NA
NA
Monitoring
leachate,
ground
water
volat iles
berm,
ground
water
volatiles ,
shellfish
cap integ-
rity,
cap con-
taminants
cap bio-
turbat ion
Remedial
Response
leachate
treatment
ground water
treatment,
sed iment
remova1
slurry
wa 11
dewatering
berm,
sediment
removal
add cap
materials
Total Number
of Available
Options 17 11 11 13 4 1
-------
cases, the largest fraction of the contaminants will be bound to sediments,
and the water will contain greater numbers and levels of contaminants than the
gas phase. Since volatiles present in the gas phase will rarely present a
concern, and since control of sediment particles is relatively well understood
and developed, the key to most projects will be the types and amounts of
soluble or easily-solubilized contaminants present. Handling of soluble
contaminants presents the greatest technical difficulties and can involve the
greatest treatment costs.
For hydraulic dredging, the relative importance of losses at various times and
from various phases during the sediment handling process is shown below,
listed in order of decreasing importance.
(1) short-term loss of sediment and water,
(2) long-term loss of water,
(3) short-term loss of volatiles,
(4) long-term loss of volatiles, and
(5) long-term loss of sediment.
For mechanical dredging, (1) and (2) may be equally important, as more easily
solubilized contaminants are retained and available for possible long-term
loss from the dredged material.
For hydraulic dredging, disposal will normally result in greater short-term
loss of sediment and water than will dredging. Mechanical dredging can result
in greater loss at the dredging site than at the disposal site. Where treat-
ment is not done or is not available, long-term loss of water can be more
important in upland situations than short-term losses due to the higher con-
taminant concentrations that are possible in the long-term discharges. For
volatiles, short-term losses may be equivalent to long-term volatilization if
in situ gas volumes are low. For open-water disposal, long-term sediment
losses can be more important than losses of volatiles.
The influence of sediment contamination on dredging, disposal, control, and
treatment decisions will be keyed to the relative magnitude of potential
contaminant releases and to the potential impacts of these losses* Based on
the above ranking of importance, short-term sediment and water loss during
disposal will be the usual first consideration and the basis for selecting
disposal method and treatment level. Concurrently, but on a secondary basis,
the contribution of dredging to this loss should be evaluated. The next,
subsequent step should be selecting appropriate treatment, monitoring, and
remedial response to address long-term loss of waterborne contaminants. Con-
sideration of items (3)-(5) above would depend on sediment and site-specific
conditions.
6-11
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Selection of dredging equipment and design of a disposal site for a given
contaminated sediment first require the application of specific tests to
assess contaminant phase partitioning and behavior, to estimate contaminant
release at various points during the handling process, and to predict contami-
nant effects under various disposal conditions. Test results are then com-
pared to predetermined standards or reference points (decisionmaking criteria,
see section 1.05) to determine where predicted contaminant behavior will
require some form of restriction or control. The purpose of the necessary
restriction(s) is to reduce (or eliminate) the concern behavior to an accepta-
ble level, thereby providing maximum containment and minimum release of
contaminants. Selecting an appropriate restriction method often requires
additional sediment testing as part of project design.
Thus, a given sediment from the Superfund site may undergo three different
test sequences:
a. testing to determine in-place hazard (is it a "problem" sediment?),
b. testing to determine if restrictions are required to dredge and
dispose the sediments in various disposal environments, and
c. testing to select and design the necessary restrictions.
The preceeding sections of this report display and compare the basic options
available for design of a restriction or control. Testing methods and
decisionmaking criteria are being developed by others (see section 1.05).
6.06 Disposal Sites. The specific disposal sites identified and discussed in
chapter 3.0 were evaluated and the results are tabulated in tables 6-4, 6-5,
and 6-6. This evaluation is based on available data and the professional
judgements of those involved in preparing this report. Telephone and personal
contacts were made with responsible officials with the Port of Tacoma, city of
Tacoma, city of Fife, Pierce County, Puyallup Indian Tribe, State of Washing-
ton, and others. These contacts were not intended to be a comprehensive
solicitation of concerns associated with dredging and disposal of contaminated
sediments in Commencement Bay, but were instead intended to identify potential
disposal sites and to obtain preliminary views on major concerns related to
these sites. Not all landowners were contacted as to the availability of
their lands, nor were assessments of the value of those lands made. The
objective of this evaluation is to develop a reconnaissance level ranking of
sites that could receive contaminated dredged material. Those sites that rank
"best" are not necessarily to be considered "recommended;" however, they show
the best promise for more detailed evaluation leading to a recommended site.
For open-water disposal sites, ease of capping was used as an evaluation
factor rather than cost of site preparation. Site preparation of open-water
sites would simply be an extension of dredging, that is, underwater dikes
could be constructed using clean sediments dredged during the course of navi-
gation maintenance. For this factor, the Hylebos/Browns Point site ranks
highest since it has the best potential for burial containment. The DNR site
6-12
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TABLE 6-4
EVALUATION OF OPEN-WATER DISPOSAL SITES
Potential Impacts to
Site Availability Distance Capacity Capping Habitat
Puyallup River
Delta 0a + + -b 0
DNR + -c + - +
*Hylebos/Browns
Point 0a + + +b ?
+ Positive - Negative 0 Neutral ? Information Needed
a DNR would have to designate site as available,
b Some site preparation might be required.
c Beyond pipeline pumping, acceptable for barge and hopper.
* Further evaluation is recommended at this time.
would have to employ the mounding technique in extreme depths. The Puyallup
River delta is very unstable; capping and containment may be impossible over
the long term. Only the DNR site is currently designated as approved for
open-water disposal; however, depending on a variety of considerations, either
or both of the other sites could be designated as well. Capacities are
essentially unlimited at all sites. The Puyallup River delta is closest to
the potential dredging sites; Hylebos/Browns Point is second. The DNR site is
outside the most economical pumping distance for Commencement Bay sediments;
although it is acceptable for barges and hopper dredges. Because the DNR site
has and is currently receiving dredged material on a periodic basis, addi-
tional adverse environmental impacts would be fewer. The instability of the
Puyallup River delta suggests that unacceptable impacts on benthic resources
would not occur, but that same instability renders capping of contaminated
sediments difficult. Little is known about the Hylebos/Browns Point site;
although it may be important bottomfish habitat. Further evaluation of the
Hylebos/Browns Point site is recommended because of the potential for more
complete containment of sediments. No further evaluation is recommended for
the Puyallup River delta.
Upland disposal sites are highly varied within the Commencement Bay area.
Depending on the volume of contaminated sedimeiit that requires removal and
disposal, one or more upland sites may ultimately be determined necessary. In
addition, individual dredgers may encounter small volumes of material that
could be disposed of upland, but timing of dredging, need to fill the site for
development, or other considerations may make use of a small site appropriate.
6-13
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TABLE 6-5
EVALUATION OF UPLAND DISPOSAL SITES
Impact to
Site Availability Pis tance Capacity Costsa Habitat
Puyallup
Mitigation
(+35 feet) - + + + ?b
*POT "D"
(+20 feet) + + 0 - +
(+35 feet) + + + + +
*Puyallup River/
Railroad
(+20 feet) 0 + +0
(+35 feet) 0 0 +
POT "E"
(+35 feet) + 0 + + +
Hylebos Creek
#1 & n
(+20 feet) ? 0 0 0 -b
(+35 feet) ? 0 + - -b
+ Positive - Negative 0 Neutral ? Information Needed
a Site preparation costs divided by cubic yard capacity of the site,
b Agency concerns anticipated.
* Further evaluation recommended at this time.
6-14
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TABLE 6-6
EVALUATION OF UPLAND DISPOSAL SITES
Site
Impact to
Availability Distance Capacity Costsa Habitat
Middle WW -
*Milwaukee WW +
*Blair WW Slips +
*Blair Graving
Dock +
Hylebos WW #1 +
Hylebos WW #2 +
0
+
+
0
0
0
0
+
+
0
+
+
+
0
+
+
0
0
Ob
+ Positive - Negative 0 Neutral ? Information Needed
a Site preparation costs divided by cubic yard capacity of the site,
b Relocation of existing marina in inner slip required.
* Further evaluation recommended at this time.
Of the upland sites, Port of Tacoma "D" and the Puyallup River/railroad sites
are the most worthy of further evaluation. Their capacities are large, the
sites are within pumping distance from a variety of Commmencement Bay dredging
sites, and the sites are sufficiently large to permit onsite treatment facil-
ities to be constructed. Because of the existence of the wetland meadow on
Puyallup River/railroad site, environmental impacts are rated negative (high
impact) in relation to the other sites being evaluated; however, a more
detailed examination of environmental effects is warranted. The Port of
Tacoma "E" is considered a good candidate due to its location relative to much
of the harbor area, but does not have capacity below +20 feet HLLW. The
proposal for wetland restoration at the Puyallup mitigation site makes future
use unlikely. Although it is not eliminated from future consideration, the
site is not recommended for detailed evaluation unless a specific need can be
identified. Hylebos Creek Nos. 1 and 2 have a good preparation cost to capa-
city ratio; however, use of these sites would displace ongoing agricultural
activity. In addition, the sites' availability is unknown and its mixed
ownership would probably require the site be acquired rather than be made
available.
6-15
-------
There are generic problems with nearshore disposal sites with regard to con-
tainment of contaminated sediments. Nevertheless, as further information is
developed, including sediment criteria, techniques for placing and retaining
contaminants in nearshore areas may be developed. Of the sites identified and
evaluated in Commencement Bay, three are not recommended for further evalu-
ation: Middle Waterway and Hylebos Waterway Nos. 1 and 2. Middle Waterway
might be useful for partial fill using contaminated sediments, but it might be
more useful dredged out and its navigational capability restored. The outer
area is still used; relocation of adjacent landowners and users to other
portions of the harbor could be expensive and difficult. Benefits do not
appear to warrant the effort. The two Hylebos Waterway sites are probably
available, but the cost of one is high in comparison to capacity, and both
sites are wetlands with high resource value to Commencement Bay. Further
evaluation at this stage does not seem warranted.
Of the remaining three sites, the Blair graving dock has relatively limited
capacity; however, its preparation costs are also quite low. The site is more
suitable for a one-time disposal and should be considered for such if the
opportunity presents itself. The Blair Waterway slips are intended to be
filled and developed in the future. They represent a large capacity and
preparation costs are reasonable. They are located centrally on the water-
front and would be able to accept sediments from anywhere in Commencement
Bay. Environmental impacts are relatively moderate; although mitigation might
be required. The largest drawback to the slips is the existing marina in the
inner slip that would need to be relocated. Likewise, Milwaukee Waterway
presents an opportunity as the port intends to fill the waterway to accommo-
date Sea-Land and to develop their own container terminal capacity. Milwaukee
Waterway has large capacity, is not presently being extensively used for
navigation, and has no adjacent users that would have to be relocated.
Further evaluation of these three nearshore sites is recommended.
Selection of a particular disposal site requires not only consideration of the
factors mentioned above but also acknowledgement of the dredge used and the
treatment to be applied following disposal. The best approach in dealing with
contaminated sediments may involve a "mixed" approach, especially where there
is a limited disposal resource and a variable level of contamination or
various classes of contaminants. For instance, sediments that contain high
concentrations of heavy metals but are low in organic contaminants can be
safely and relatively inexpensively disposed of in capped open-water sites.
Sediment that contains high organic concentrations should go to upland dis-
posal sites with their relatively high degree of control and monitoring
potential. Most sediments, of course, will fall somewhere in the middle
ground and the identification of criteria that are to be met becomes a most
important task. If levels of contaminants and criteria specific to those
levels can be developed, a more flexible approach may be possible.
One useful approach is selective dredging and disposal. Since treatment costs
are very expensive, it would be prudent to treat only those volumes of sedi-
ment that meet or exceed the levels that trigger the need for treatment.
Further, segregation of the types and levels of contaminated sediments would
6-16
-------
allow decisionmakers to establish and match criteria specific to the types and
amounts of contamination present in each sediment class. And finally, selec-
tive dredging and disposal allows maximization of a limited disposal capa-
city. If there is only capacity for 250»000 c.y. of highly contaminated
material, it is inefficient and expensive to fill that site with 25,000 c.y.
of highly contaminated sediments mixed with 225,000 c.y. of relatively cleaner
material. However, in order to accomplish this, sediment characterization
must be done to finer levels than is typically done for most dredging proj-
ects. At the same time, this characterization and subsequent segregation must
bear in mind the precision of the dredging equipment employed (table 6-1).
Having developed suitable criteria, horizontal and vertical sediment charac-
terization can be done to levels that dredging equipment can selectively
remove.
Very contaminated sediments should be processed at a treatment facility to
remove the cleaner fraction of the sediments, typically the coarser material.
This coarse material, often comprising the bulk of the total sediment volume,
can then be reused as capping material, open-water disposed, or used as upland
fill. The remaining fines can be settled out by a number of techniques and
this reduced volume treated or placed in an appropriate holding facility.
This option requires hydraulic dredging and possible treatment of effluent.
The cost of segregation and rehandling may be compensated for by the reduced
cost associated with treating and confining less contaminated sediment.
Another very useful approach is to realize that the costs associated with even
the simpler dredging, disposal, and treatment methods are substantial, and
when viewed from the perspective of an individual, a small industry, and even
a single agency, can be staggering. It is possible that a single, comprehen-
sive disposal site and treatment facility could be established that would be
used by those with dredging requirements. The site(s) would be managed by a
single entity and would be designed to meet criteria that had been established
by a regional or national management plan. Conceptually, the high initial
cost for acquiring and developing the disposal site and any associated treat-
ment facilities could be spread between the dredgers and prorated at an unit
cost per each cubic yard disposed. This solution would amortize the expense
of initial construction over time as well as spreading that cost among users;
and it would likely result in less land being impacted and therefore fewer
disruptions in land use. Development of such a management plan and/or dis-
posal facility with a managing entity would be a complex and difficult task.
For large volumes of contaminated material, such as occurs in Commencement
Bay, it may be the only practicable solution.
6.07 Information Needs and Recommended Study. Many of the methods and
techniques addressed in this report merit further study, research, and
experience in terms of their application to, and relative contribution in,
handling of contaminated sediments. A few of the more noteworthy and priority
items are identified below.
As pointed out by Thibodeaux (1984, appendix 2a), there can be a big differ-
ence between contaminant mobility as predicted by partitioning coefficients
and contaminant mobility as seen in the field. In situ measurement of
6-17
-------
contaminants in interstitial waters would verify partitioning predictions.
Better quantitative predicting of mobility can be obtained by conducting pilot
scale laboratory tests to develop empirical relationships of contaminant
mobility under various disposal conditions in combination with the use of
mathematical models to predict this mobility. Tests to measure long-term
contaminant mobility for the three disposal methods and resulting conditions
and developing first stage modeling of mobility should be considered for the
near future.
Additional experience and prototype work is needed for several aspects of
aquatic disposal of contaminated sediments. Capping of contaminated sediments
should be demonstrated using equipment, sediments, and material available in
Puget Sound. Experience in placing underwater clay liners is needed. The
vertical diffuser should be demonstrated in the United States.
Loss of volatile contaminants through degasser systems on hydraulic dredges
should be investigated. Potential loss should be estimated by obtaining field
information on the volume of gas in the sediments in situ. Actual loss should
be studied by monitoring of degasser discharges.
Additional planning will be needed before the list of potential disposal sites
can be pared down to those that are probable for designation. The generic
information needs identified in chapter 3 for each type of disposal site
should be pursued as part of ongoing planning in Commencement Bay.
The availability of special-purpose dredges could be a major consideration in
their use in Commencement Bay. Due to the advantages that these plants offer,
specific determinations of their availability are warranted at this stage of
planning.
The common theme of dredging, disposal, and treatment discussions above is the
identification of pertinent decisionmaking criteria. These should define
testing methods and interpretation of test results to determine when certain
dredging and disposal options are appropriate and required. Closely associ-
ated with the interpretation of test results is the need for better informa-
tion on the long-term effects of contaminant release to the receiving
environment. Development of criteria represents the central link between
available disposal sites, the extent and types of sediment contamination, and
the navigation and Superfund needs to move that sediment. The criteria will
allow assembly of the components of a dredging job: type of dredge, disposal
site, and treatment levels, and are at the core of a management plan for
Commencement Bay. Therefore, development of decisionmaking criteria should
receive primary attention in any future efforts.
6-18
-------
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Myers, A. C. , 1979. "Summer and Winter Burrows of a Mantis Shrimp, Squilla
empusa, in Narragansett Bay, Rhode Island (USA)." Est. Coast. Mar. Sc.,
Vol. 8, pp. 87-98.
Neal, R. W., et al, 1978. "Evaluation of Submerged Discharge of Dredged Mate-
rial Slurry During Pipeline Dredge Operations." Technical Report D-78-44 ,
U.S. Army Engineer Waterways Experiment Station, Vicksburg, MS.
O'Conner, J. M., 1983. Evaluation of Capping Operations at the Experimental
Mud Dump Site New York Bight Apex, 1980. Synthesis Report for U.S. Army
Engineer Waterways Experiment Station, Vicksburg, MS.
Palermo, M. R., In preparation. "Field Evaluations of the Quality of Influent
and Effluent from Confined Dredged Material Disposal Areas." Technical
Report in Preparation, U.S. Army Engineer Waterways Experiment Station,
Vicksburg, MS.
7-4
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Palermo, M. R., 1984. "Interim Guidance for Predicting the Quality of Efflu-
ent Discharged from Confined Dredged Material Disposal Areas," Draft
Engineer Technical Letter, Office, Chief of Engineers, Washington D.C.
Palermo, M. R., 1983. "Interim Guidance for Conducting Modified Elutriate
Tests for Use in Evaluating Discharges from Confined Dredged Material
Disposal Sites." Draft Engineer Technical Letter, Office, Chief of
Engineers, Washington D.C.
Palermo, M. R., R. L. Montgomery, and M. Poindexter, 1978. "Guidelines for
Designing, Operating and Managing Dredged Material Containment Areas."
Technical Report DS-78-10, U.S. Army Engineer Waterways Experiment
Station, Vicksburg, MS.
Pavlou, S. P., and D. P. Weston, 1984. Initial Evaluation of Alternatives for
Development of Sediment-Related Criteria for Toxic Contaminants in Marine
Waters (Puget Sound), Part II: Development and Testing of the
Sediment-Water Equilibrium Partitioning Approach. JllB Associates under
U.S. EPA Contract No. 68-01-6388, Washington, D.C.
Pohland, F. G., 1980. "Leachate Recycle Landfill Management Option." Journal
of Environmental Engineering Proceedings of the American Society of Civil
Engineers, Vol. 106, EE6 (1980), pp. 1057-1069.
Prengle, H. W., Jr., C. E. Mack, R. W. Legan, and C. G. Hewes, III, 1975 .
"Ozone/UV Process Effective Wastewater Treatment." Hydrocarbon
Processing, pp. 82-87 (October 1975).
Roe, J., et al, 1970. "Chemical Overlays for Sea Floor Sediments." Presented
at the Second Offshore Technology Conference, Houston, TX.
Schroeder, P. R. , 1983. "Chemical Clarification Methods for Confined Dredged
Material Disposal." Technical Report D-83-2, U.S. Army Engineer Waterways
Experiment Station, Vicksburg, MS.
Schroeder, P. R. , A. C. Gibson, and M. D. Smolen, 1983. The Hydrologic Evalua-
tion of Landfill Performance (HELP) Model; Volume II. Documentation for
Version 1. Draft Technical Resource Document, U.S. Environmental
Protection Agency, MEKL, Cincinnati, OH.
Shafer, R. A., et al, In preparation. Properties of Landfill Liners and Covers
and Application to Army Landfills. U.S. Army Construction Engineer
Research Laboratory, Champaign, IL.
Shafer, R. A., et al, 1983. Treatment of Landfill Leachate at Army Facilities,
Report N-155. U.S. Army Construction Engineer Research Laboratory,
Champaign, IL.
Simmers, J. W., R. G. Rhett, and C. R. Lee, 1983. "Application of a Terres-
trial Animal Bioassay for Determining Toxic Metal Uptake from Dredged
Material." Proceedings» International Conference on Heavy Metals in the
Environment, Heidelberg, Germany.
7-5
-------
Takenaka Kometen, Ltd., 1976. "Recent Developments in Dredged Material Stabil-
ization and Deep Chemical Mixing in Japan." Promotional Brochure, Tokoyo,
Japan.
USACE. In press. Management Strategy for Disposal of Dredged Material, U.S.
Army Engineer Waterways Experiment Station, Vicksburg, MS.
USACE. In press. Sediment Resuspension Characteristics of Selected Dredges,
ETL 1110-X-XXXX, Washington, D.C.
USACE. 1983. Dredging and Dredged Material Disposal, EM 1110-2-5025,
Washington, D.C.
USACE. 1983. Chemical Clarification Methods for Confined Dredged Material
Disposal, U.S. Army Engineer Waterways Experiment Station, Vicksburg, MS.
Wang, C., and K. Chen, 1977. Laboratory Study of Chemical Coagulation as a
Means of Treatment for Dredged Material. Technical Report D-77-39 , U.S.
Army Engineer Waterways Experiment Station, Vicksburg, MS.
Whalen, T. 1982. "Dredging Program: Equipment and Costs," Water Resources
Support Center, Fort Belvoir, VA.
Widman, M. , and M. Epstein, 1972. "Polymer Film Overlay System for Mercury
Contaminated Sludge—Phase I." No. 16080 HTZ, U.S. Environmental
Protection Agency, Washington, D.C.
Windom, H. L. , 1972. "Environmental Aspects of Dredging in Estuaries."
Journal of the Waterways, Harbors, and Coastal Engineering Division, ASCE,
No. wwA, November 1972.
Yu, Kar, Y and Chen, Y. Kenneth, 1978. Physical and Chemical Characterization
of Dredged Material Sediments and Leachates in Confined Land Disposal
Areas. Technical Report D-78-43 , U.S. Army Engineer Waterways Experiment
Station, Vicksburg, MS.
7-6
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APPENDIX 1
A SOLUBILITY AND MOBILITY CLASSIFICATION OF ORGANIC
CHEMICALS IDENTIFIED IN COMMENCEMENT BAY SEDIMENTS
-------
APPENDIX 2
REVIEWS OF LONG-TERM CONTAMINANT MOBILITY FOR VARIOUS
DISPOSAL OPTIONS IN COMMENCEMENT BAY
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APPENDIX 2
TABLE OF CONTENTS
a. Review by Dr. Louis J. Thibodeaux, University of Arkansas
b. Review by Dr. Paul V. Roberts, Stanford University
-------
Louis J.Thibodeaux, Ph.D.
PROFESSOR
Department of Chemical Engineering
University of Arkansas, College of Engineering • Fayetteville, Arkansas 72701
Engineering Building, West Dickson Street, Room 331 • (501) 575-4951 • Home (501) 521-3837
January 4, 1984
Dr. Keith Phillips
U.S. Army Engineer District, Seattle
NPSEN-PL-ER
P.O. Box C-3755
Seattle, Washington 98124
Dear Keith:
Enclosed is the letter report that provides my opinion on the lona-term
mobility of sediment-related contaminants under various disDOsal conditions
in Commencement Bay. If you have any questions or would like more details
on some aspects please give me a call.
Thanks for the opportunity to be a part of this effort; it is a very
interesting problem.
Sincere!v
Louis J. Tnibodeaux
Professor
krd
Enclosure
-------
-LETTER REPORT —
Expert Opinion on Disposal Options for
Contaminated Dredge Material from
Commencement Bay, Tacoma, Washington
Louis J. Thibodeaux, P.E.
January 3, 1984
The Seattle District, U.S. Army Corps of Engineers, under agreement with the
State of Washington Department of Ecology, is evaluating alternative dredging
methods, disposal sites and site control (treatment) practices for contaminated
sediment derived from the Commencement Bay Nearshore/Tideflats Superfund Site,
Washington. Disposal options available in Commencement Bay include: subaquatic
disposal (with or without capping), partially aquatic disposal
(intertidal/subtidal fill) and upland disposal. There are insufficient empirical
data on the Commencement Bay sediments to quantitatively distinguish differences
between these disposal options in terms of long-term contaminant mobility. In
order to distinguish contaminant containment efficiencies of these disposal
options and recommend specific disposal sites and treatment practices, a review
of Commencement Bay sediment and contaminant data with respect to contaminant
mobility is needed.
There appears to be some confusion about the term mobility. Calhoun (1983),
adopting from Swann, et. al., uses the term in a thermodynamic sense. He
classifies the organic compounds by mobility class when in fact his classifica-
tion reflects the degree to which the organic species partition onto the soil
sediment organic fraction during a reversible equilibrium sorption environment.
The proper coefficient should be the desorption coefficient measured under sea-
water salt concentration conditions. Even this coefficient is inturn related to
mobility in a complex manner.
-------
Mobility implies a rate process and a time, either implicit or explicit,
need be quantified. Mobility or transport is a function of the chemical spe-
cies, the solvent (water), the type of soil/sediment matrix, the physical state
of the system, chemical concentration levels and certain geometric factors.
These seven factors are inturn subdivided into quantifiable or specific values
as shown in Table 1. It is apparent from this list that the partition coef-
ficient addresses only one small facet of the mobility question.
There are several physical/chemical/biological processes that can and do
result in contaminant mobility (or transport). When considering these mobility
aspects it is assumed that the issue is the question of contaminants within a
sediment/water environment. Contaminants can be mobilized and move between two
points in space by the following mechanisms:
1. diffusion of dissolved species down a concentration gradient and through
the sediment-water interface,
2. convective and dispersion of dissolved species (and fines) due to the
water flow through the sediment,
3. bioturbation in the top layer of the sediment
4. scour and suspension of surface sediment particles due to bottom water
currents,
5. gas generation and ebullition within and through the sediment/water
interface.
All of these mechanisms can be active in some of the disposal options while only
one or two may be active in others. The point is that there will always be some
active transport mechanisms operative in all disposal options and that none of
the options will provide a complete isolation of the contaminants from the
Commencement Bay ecosystem. It is likely that one or more of the options will
provide sufficient containment and acceptable levels of contaminant mobility.
2
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Application
Table 1 provides a ranking in order-of-magnitude steps of solubilities of
the organic chemicals considered in this report. The ranks correspond to the
column headed "solubility" in Table 3. The verbal descriptors are chosen
arbitrarily, indicate only relative solubilities, and are specific to this
report.
Table 2 ranks the mobility of chemicals in soils and sediments according
to their partitioning behavior between water and soil or sediment organic
carbon. The numerical ranks correspond to the column headed "mobility" in
Table 3.
The arrangement of Table 3 is by analytical preparation type, i.e.,
Volatiles, Base/Neutrals, etc., with chemicals ranked within each type by
decreasing solubility and mobility. Chemicals which are ranked similarly in
each type may be considered to behave similarly in their solubility and
mobility properties.
These data are provided with the reservation that pure water solubilities
of hydrophobic organic chemicals do not accurately represent their behavior in
aqueous environmental systems. Mobility calculations consider some of the
factors in addition to solubility influencing movement of chemicals in the
environment. Therefore, mobility calculations provide additional useful
information for classifying chemicals in terms of potential environmental
concern.
3
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Mobility of contaminants can be assessed in two ways. Field techniques
usually involve contaminant concentrations measurements and phase (i.e., water
or sediment) movement measurements (Pavlou, et. al., 1982). The field tech-
niques available for addressing contaminant mobility have some model concepts,
either implicity or explicitly associated with the methodology or instrumen-
tation. The other means of addressing questions of contaminant mobility is by
the application of models. These models are primarily mathematical constructs
involving the factors listed in Table 1. These constructs can be elaborate com-
puterized assemblages such as the EXAMS (Exposure Analysis Modeling System)
model or they can be simple vignette models which focus on isolated events that
account for a few dominant transport/fate mechanisms. Models usually reflect
much laboratory simulation work and ocassionally receive complete field testing
and verification. However, they are being used extensively because of low cost
and relatively high confidence interval.
The field work that has been performed in Commencement Bay is inadequate to
quantify the rate of mobility of contaminants from the "hot spots" around the
various waterways into the near regions of the Bay and the farther regions of
the Sound. The use of the term mobility here refers to the mass of selected
chemical species and/or all components leaving the waterways per day. The field
work that has been reported on is water currents (both surface and subsurface)
and directions in the Bay and in the individual waterways and chemical con-
centrations in the sediment and in the water. These field measurements reflect
the fact that contaminants have been mobilized from the waterways and that the
Bay currents are present to move the contaminants into the Bay and further
afield to the Sound, but the data does not allow flux rates of individual species
of total mass flux rate to be quantified. However, the available field data
does provide a basis to commence the use of models that will address contaminant
4
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mobility questions.
It seems to me that the quantification of chemical release rates is one of
the preferred method of evaluating disposal options. The release rates asso-
ciated with the base case (i.e., the waterways contaminant situation as it exist
now, before clean-up) need be made in order to assess the effectiveness of any
proposed clean-up and disposal plan. Otherwise the relative merits of the
variously proposed plans will be done on a purely qualitative basis. Since the
field work necessary to completely quantify rates of mobility for the base case
and proposed disposal options is incomplete and obtaining completely satisfac-
tory data will be exceedingly costly and time consuming, it seems to me that
fate/transport models need be utilized at this time to answer questions of
clean-up/disposal options and relative degree of isolating the contaminants from
the Bay ecosystem.
The key question, as I see it, is which disposal options will isolate the
contaminants from the environment to such a degree that the residual chemical
release rates will be significantly lower than the present release rates as to
not significantly effect the biota in the Bay to a deleterious extent. At pre-
sent there are data gaps, insufficient data analysis and an insufficient
modeling, effort and analysis, to quantitatively distinguish between disposal
options in terms of mobility. In order to distinguish contaminant efficiences
of the proposed and other disposal options the following preliminary design
scenario, data acquisition and fate/transport modeling tasks should be
undertaken:
A. Preliminary Design Scenario Tasks
1. decide on likely specific location for disposal options (i.e., where in
waterway, in Bay, upland, etc.)
5
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2. decide on disposal configuration and manner at each location (i.e.,
water depth, cover thickness, lateral extent, etc.),
3. estimate the mass (or volume) of sediment involved in clean-up,
4. decide on if and how the various contaminated sediments will be combined
into highly, medium or slightly contaminated portions for disposal, and
5. choose selected individual chemical species that are characteristic of
the various classes of organic compounds and metals for specific
modeling studies.
B. Data Aquisition Tasks
1. review the sediment contaminant data and choose reasonable concentration
levels for the selected chemicals to be modeled,
2. review the factors presented in Table 1, paying particular attention to
those factors with little or no (disposal) site specific information,
and
3. review the model demands (next section) for particular data requirements
of the algorithms.
C. Fate/Transport Modeling Tasks
1. choose an appropriate fate/transport model such as EXAMS, that contains
conical element options that will correspond to the various disposal
opti ons
2. if no such model is available then effort need be devoted to assemble
vignette models for each disposal option, and
3. perform model simulations that deliver (either directly or indirectly)
the rate (g/h) of emission of individual chemicals associated with the
various disposal options. The appropriate emission rates are those that
relate the amoung leaving the contaminated sediment disposal sites and
6
-------
re-entering the Bay. Ancillary outputs include contaminant life-time or
residence time within the disposal cells, fraction converted by reaction
(i.e., hydrolysis, chemical, biological), the fraction irreversibly
sorbed and the fraction transported out.
The disposal options that should be considered in the modeling effort are as
follows:
1. leave contaminated sediment in-place (serves as the "base case"),
2. sub-aquatic contaminated sediment disposal at a deep-water site without
capping,
3. sub-aquatic disposal at deep-water site with caping,
4. sub-aquatic in a waterway (Rotterdam-Putten Plan) with clay liners
(Kleinbloesem and van der Weijde, 1983),
5. partial aquatic (nearshore fill above high tide),
6. upland, and
7. combination of the above considering high, medium and low sediment con-
taminant levels.
Figures 1 through 6 illustrate the basic concept of each disposal option and
indicate transport direction (arrows) of mobility mechanisms.
Mobility mechanisms that need be considered in the various modeling task are
indicated on the illustration of each disposal option. Figure 1 illustrates the
transport pathways for mobile contaminants as they presently exist in the water-
way. The transport processes are: scour of fines from the silt surface, gas
ebullition, bioturbation, diffusion and convection. Groundwater infiltration
from underneath originates in the fill zones that separate the waterways.
The Rotterdam-Putten Plan disposal option is illustrated in Figure 2. This
option enjoys a fewer number of transport mechanisms. Bottom water currents
7
-------
flowing over a wavy sediment bed can induce pore water currents within the upper
layers of the sediment. Due to the dead-end nature of the waterways the
currents may be small and this mechanism of convective transport is not
illustrated. It is illustrated in the sub-aquatic disposal options figures.
The model studies should have two subelements that reflect the transient or
start-up period of the mobility question and the steady-state or quasi steady-
state period. For example, in the Rotterdam-Putten Plan option where con-
taminated sediment is buried in a lined "vault" within the waterway, there will
be a period of time that will lapse before quantities of the contaminants will
reappear at the sediment-water interface. Once all the sorption sites along the
transport pathway are filled then the process enters the steady-state mode and
chemical quantities re-entering the waterway assumes the highest values.
The deep-water disposal options are illustrated in Figures 3 and 4. The
without capping option has essentially the same transport mechanisms as the
"base case" except that the magnitude of the fluxes will be different. The sand
cap that can be placed upon the deep-water disposed sediment will retard the
transport somewhat. Likely gas generation and bioturbation will be reduced
significantly.
The partial aquatic disposal option is illustrated in Figure 5. Water con-
vection due to tidal pumping will likely be a dominant and efficient mechanism
for extracting contaminants from the contaminated sediment cell. Groundwater
and rainwater leachate and diffusion processes will be present. Volatilization
will occur from the unsaturated sediment zone, but this fraction will not likely
re-enter the waterway. Oxidation processes will be active in the unsaturated
zone releasing metals that may otherwise be in a sorbed state.
The upland disposal option is illustrated in Figure 6 and has volatilization
and leachate transport mechanisms. Oxidation processes will likely be more
8
-------
active than in the partial aquatic disposal option.
All things considered a qualitative evaluation based on the number of active
transport mechanisms and the control and effectiveness of the disposal operation
and containment would suggest that the Rotterdam-Putten Plan is the preferred
from a mobility standpoint. The next to best option is the deep-water with
capping. A reasonable compromise would be to bury the highly contaminated sedi-
ment in the waterway and place the reinaincler in deep water with a cap.
9
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LITERATURE CITED
Calhoun, C. C., "A Solubility and Mobility Classification of Organic
Chemicals Identified in Commencement Bay Sediments", Letter to Keith
Phillips, WES, Vicksburg, MI, October 26, 1983.
Pavlou, S. P., et. al., Release, Distribution, and Impacts of PC8 Induced by
Dredged Material Disposal Activities at a Deep-Water Estuarine Site, Env.
Int., 7, 99-117, 1982.
Kleinbloesem, W. C. H., and R. w. von der Weijde, A Special Way of Dredging
and Disposing of Heavily Polluted Silt in Rotterdam, Paper M2, World
Dredging Congress, Mandarin Singapore, Aug. 19-22, 1983.
11
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Environmental Engineering & Science
DEPARTMENT OF CIVIL ENGINEERING
II RM AN I NGINI I RING ( I ATI R
STANFORD UNIVERSITY
PAliV ROR.RTS STANFORD, CALIFORNIA 94W5
I'fi i I <-r nl I.Ht tlljl In SIHtt'i (4 } S) 1 i) ' s
31 December 19^3
Mr. Keith Phillips
Seattle District
Corps of Engineers
P.O. Box C-3755
Seattle, Washington 9812^
Dear Mr. Phillips:
At your request, I have reviewed the available information on alternatives
for disposing of contaminated sediments from Commencement Bay. This work
was carried out under P.O. DACA 67-$+-M-09^7. This letter report represents
the result of my evaluation effort under that agreement.
Of the several options proposed, capped deep-water disposal appears to offer
the best assurance of isolating the contaminated sediments in such a way that
human populations will not be exposed to the contaminants in concentrated form.
However the technology of controlled disposal and capping of the deposit in
deep water is largely unproven. Extreme care and a substantial measure of
technological improvement will be necessary to prevent dispersal of the
contaminants throughout Commencement Bay and Puget Sound.
Both of the other two groups of alternatives, upland disposal and near-shore
disposal, pose more immediate environmental and health risks than does deep-
water disposal. Given the hydrologic conditions in the Tacoma region, it
seems inexorable that serious pollution of groundwater and contiguous water-
ways would result from disposal landfills at upland sites in the Port of
Tacoma vicinity. On the other hand, if near-shore disposal were chosen,
there would be continual exposure of the contaminated sediments to large
volumes of water as a result of tidal fluctuations, with direct impact on the
shallow-water portion of Commencement Bay.
The key to the successful isolation of contaminated sediments in deep water
is the ability to deposit sediments and cover material directly onto the
bottom in a precise manner and with an exit velocity sufficiently low to
prevent escape of fines as turbidity. Such a technique was described and
recommended by Mr. Norman Francinques at the 1^ December meeting on sediment
mobility issues. The method entails depositing the sediment through a
specially designed diffuser, which achieves horizontal egress of the sediments
at low velocity, 0.3 to OA m/s. This technique has been applied effectively
for disposing of contaminated sediments in Rotterdam Harbor, as detailed in
a paper distributed by Mr. Rrancinques at the l*f December meeting. However,
a major difference between the Rotterdam application and the proposed
Commencement Bay application must be recognized: at Rotterdam the water depth
was approximately 10m, whereas the deepwater disposal sites in Commemcement
Bay lie at depths of 30 to 150 m. Moreover, in the Rotterdam operation, the
-------
page 2
cap material was not deposited with the diffuser described above, but rather
dumped beside the previously deposited sediments and drawn over the deposit
by means of a bottom leveler. This latter method seems poorly suited for
use at the depths characteristic of Commencement Bay. The reason given for
not using the diffuser to place the cap material in Rotterdam Harbor is that
the clay cap material was too lumpy to be pumped. Clearly, the amenability
to pumping should be a a major criterion in choosing the cap material.
From the viewpoint of scour resistance as well as pumpability, a well-sorted
sand might be preferable to clay as capping material.
To assess deepwater disposal options, more complete information on current
velocities is essential. Strong near-bottom currents would disperse fines
during disposal of the contaminated sediments, and would resuspend uncapped
sediments or deplete the cap by scouring after disposal. The available
information on current velocities is inadequate,l'or evaluation of deepwater
disposal alternatives. The most complete study' to date concludes that
"it is possible thi near-bottom currents might be large enough to resuspend
bottom sediments". The same study indicates that the dominant flow is along
the bay shores, particularly the south shore, where near-bottom current
velocities on the order of 20 cm/s were observed. Moreover, it was found
that deep water transits the bay in about a day, indicating that soluble
contaminants would be rapidly disseminated if exposed.
The question of transport of fine sediments during disposal, or resuspension
of exposed sediments, is critical to the efficacy of deepwater disposal as a
containment strategy. Although the sediments are relatively coarse-grained,
consisting predominantly of sand, there are substantial amounts of fines.
Silt fractions range from 1 to 50 percent, and clay fractions from ^ to ^+5
percent. Positive correlations between fines content and ignition loss
point toward the fine fractions having higher organic contents than the
sand, as expected. There are no data available on the distributions of
hazardous contaminants according to particle size, but it can be assumed
that the contaminants associated with particulates are highly concentrated
in the fine fractions. Hence, dissemination of fine particulates during
disposal would cause disproportionate dissemination of the contaminants of
concern. More data are needed on the contaminant concentrations of the silt
and clay fractions.
The fraction of organic matter in the sediments is crucially important,
because of the known propensity of hydrophobic organic contaminants to
partition into organic phases. As a first approximation, it can be assumed
that sorption onto sediments from the aqueous phase obeys a linear equili-
rium relationship, and that thj| sorption coefficient of a sediment is propor-
tional to its organic content, as measured by organic carbon. Further, the
sorption coefficient is proportional to the hydrophobicity of the organic
contaminants, as measured by their octanol-water partition coefficients. The
organic content of Port of T«a,coma waterway sediments is virtually unknown;
only a few crude measurements, of volatile solids content, have been made.
Dames and Moore (letter Of 2 September 1970) contend that the organic content
of Blair Waterway sediments is "considerably less than one percent." Several
measurements of volatile solids by Laucks Testing Laboratories indicate organic
13
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page 3
contents of 0.8 to 2.6 percent in Blair, 0.8 to ^.3 in Ijdtcum, and 1.9 to
7.0 percent in Hylebos waterway. Because the organic fraction typically
is comprised of kO to 50 percent carbon, we can surmise that the organic
carbon content of Port of Tacoma waterway sediments is in the range of
0.5 to 3 percent, with values for the more heavily contaminated sediments
tending to be toward the upper end of the range. Accordingly, sediment-
water partition coefficients may be expected to range from approximately
1:1 for the least hydrophobic contaminants identified (e.g. chloroform and
trichloroethylene) to 10,000:1 for the most strongly hydrophobic contami-
nants (e.g. DDT, polynuclear aromatic hydrocarbons, and polychlorinated
biphenyl isomers).
It must be recognized that the bulk of the organic matter in the sediments
has yet to be identified. For example, in the most highly contaminated
sediments of Hylebos Waterway, the organic content is on the order of
20 to 70 g/kg, but specific organic analysis has identified a total of only
0.03 g/kg. Of course, this comparison is not strictly permissible, because
the analyses were performed on different sediment samples, but the fact
remains that by far the greater portion of organic matter is unaccounted
for, certainly more than 99 percent. What is the nature and provenance of
the uneharacterized portion of the sediment organic matter? Can the bulk
of the organic matter be assumed to be innocuous, simply because its con-
stituents are not amenable to analysis by a given priority pollutant protocol?
It is likely that some of the uneharacterized organic matter is of natural
origin, but the elevated organic content of contaminated sediments compared
to background levels indicates that most of the organic content is anthropo-
genic. A large portion is likely to consist of fuel oil fractions and
their decomposition products. Further work is needed to characterize the
unidentified organic matter, but complete characterization is not attainable
with presently available analytical techniques.
There is some possibility of loss of volatile organic constituents to the
atmosphere during sediment dredging, transport, and disposal. This danger
is greatest under conditions of intimate air-water contact and high energy
dissipation. In this regard, the critical point is the extent of gas evolu-
tion, especially during dredging. The dimensionless air:water partition
coefficients are on the order of 0.01 to unity for the organic compounds
specifically identified in the Tetra Tech report. Of these compounds, the
most volatile is trichloroethylene, with an air:water partition coefficient
of 0.5; losses as great as 10 to 20 percent might be expected if substantial
gas evolution occurs (i.e., equal volumes of gas and sediment).It might be
prudent as an occupational safety measure to collect the evolved gas and pass
it through an adsorber filled with activated carbon or equivalent gas-cleaning
agent.
To prevent diffusive escape of contaminants after disposal, the thickness of
both the sediments and the cap should be as great as feasible. This argues
for minimizing the surface area of the disposal site by disposing into an
underwater pit. Seemingly, there is a natural site with these characteristics
in Commencement Bay. Along the northeast shore near the present barge
storage area is a natural depression that may be suitable for disposing of
contaminated sediments. Disposing into such a natural depression would
14
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page k
enhance containment in several ways. The horizontal containment on all sides
would hinder dispersal of fines during disposal, and would facilitate placing
the cap. The relatively great depth of sediment deposit attainable in this
situation, approximately 30m, would assure a low surface-to-volume ratio
that would minimize diffusive transport of contaminants into the water column
and hence assure long-term containment. The low surface-to-volume ratio
also would reduce the amount of capping material required to achieve a given
cap thickness. Also, depositing the sediments into a pronounced depression
would facilitate subsequent locating of the wastes for monitoring purposes,
because bathymetry would provide positive identification. Moreover, that
particular site affords the practical advantage of being at lesser depth
than the present deepwater disposal site in the middle of Commencement Bay.
Nevertheless, the depth of the prospective operation (30 to 60 m) poses a
technological challenge. To this reviewer's knowledge, precise, nondispersive
placement of sediment and cap at that depth has yet to be demonstrated. The
above-mentioned site should be carefully studied with respect to bathymetry,
near-bottom current velocities, biological impacts, and potential conflicts
with other uses. The availability of suitable, uncontaminated capping material
should also be ascertained. The cap thickness should be designed for an
average of at least one metre to alleviate the effects of irregularities
in deposition, scouring by currents, and bioturbation.
In summary, I believe that capped deepwater disposal is the least objectionable
alternative for disposing of contaminated sediments from the Port of Tacoma.
If confinement can be achieved by depositing the sediments in a bottom depres-
sion followed by capping, relatively secure containment can be assured. Before
that alternative is chosen, however, it must be demonstrated at Commencenent
Bay that the sediments can be accurately deposited in a confined bottom area
without loss of fines, that the deposit can be uniformly capped with clean
cover material in sufficient thickness, and that the cap's integrity can be
effectively monitored.
Demonstrating the feasibility of the preferred alternative - capped,deepwater
disposal - will entail a substantial commitment by the Corps of Engineers.
Only a thorough, onsite demonstration under the conditions of the prospec-
tive Commencement Bay disposal operation would suffice.
Paul V. Roberts,PhD
15
-------
APPENDIX 3
TREATMENT CALCULATIONS
16
-------
INTRODUCTION
This appendix provides base calculations and assumptions for many of the costs
displayed in Chapter 5.0.
17
-------
EFFLUENT FLOW RATE
For 24" Dredge Working 10 hrs/day:
Q = (19,748 gpm)(60 min/hr)(10 hr/day)(l x 10~6) = 11.85 mgd
say 12 mgd
Production Rate for 24" Dredge: 900 yd^/hr
1,000,000 yd3 = 1,111 hrs
900 yd^/hr
Operating Time Per Day: 10 hrs
1,111 hrs _ 111 days
10 hrs
Treatment will be needed 24 hrs/day for a period of 111 days. Say 4 months.
Dredging costs for 24" - pipeline suction = $1.50/yd3
For 1,000,000 yd3 (? $1.50/yd3 = $1,500,000.00
18
-------
PRIMARY CONTAINMENT AREA
Primary containment area design is discussed in EM 1110-2-5006 (Department of
Army, 1980). As a preliminary design, the area is designed based on storage
requiremen ts.
Assume:
Volume of Settled Material = 1.7 x 10-^
Depth of Settled Material = 12 ft
Minimum Ponded Depth = 2 ft
Required Area Based on Storage Area =
1.7 x 109 L _ 115 acres
(28.31 L/ft3)(l2 ft)(43 ,560 ft2/acre)
-------
POLYMER FEED SYSTEM
Polymer Feed Design:
Assume:
Sediment Volume = 1,000,000 yd^
Sediment Concentration (In Situ) = 900 g/1
Specific Gravity = 2.68
Dredged Material Slurry Concentration = 150 g/1
Dredge Pipeline Size = 24"
Average Concentration of Settled Material = 400 g/1
Specific Weight of Polymer = 1.1 kg/1
Polymer Feed Concentration = 20 g/1
Required Polymer Dosage = 5 mg/1
Average Influent Flow Rate = 12 mgd of 18.57 cfs
1. Volume of Inflow =
(1,000,000 yd3)(900 g/1)(764.4 l/yd3)/(150 g/1) = 4.6 x 109 L
2. Volume of Settled Material =
(4.6 x 109 L)(150 g/1)/(400 g/1) = 1.7 x 109 L
3. Volume to be Treated =
4.6 x 109 - 1.7 x 109 = 2.9 x 109 L
4. Volume of Polymer Required, gal =
(5 mg/1)(2.9 x 109 l)/(1.1 kg/1)(3.785 L/gal)106 mg/kg = 3,480 gal
5. Pounds of Polymer Required =
(3,480 gal) (3 .785 L/gal) (1.1 £&¦) (20,205 lb/kg) = 31,950 lb
Concentrated Polymer Flow Rate =
(18.57 cfs)(5 mg/1)(28.31 L/ft3)/(l.l g/ml)(l,000 mg/g) - 2.17 ml/sec
¦ 0.0344 gpm
¦ 49.6 gpd
Polymer Feed Tank Volume =
(49.6 gpd)(2 days) = 99.2 gal
Dilution Water Pump Rate m
2 (1.1 g/ml)(1,000 ml/1)(0.0344 gpm)/(20 g/1) - 3.784 gpm
20
-------
MUD PUMPING
Volumetric Pumping Rate, gpd
(0.5 - 0.03)g/1 x 18.57 cfs x 28.31 L/day x 86,400 sec/day / (3.785
L/gal)(88 g/1) = 64,100 gpd or 45 gpm
21
-------
SECONDARY SETTLING BASIN
Secondary Settling Basin:
As s ume:
Primary Effluent Solids Concentration - 500 mg/1
Secondary Effluent Solids Concentration = 30 mg/1
Volume to be Treated = 2.9 x 109 L
Depth of Basin = 6 ft
Average Flow = 18.57 cfs
Depth of Storage = 3 ft
Depth of Ponding = 2 ft
1. Volume of Settled Treated Material:
Mass of Settled Material =
(0.5 - 0.03)g/l x 2.9 x 109 L = 1.36 x 109 g
Average Concentration of Settled Material =
((2 x 50 g/1) + 25 g/l/ft x 3 ft) / 2 = 88 g/1
Volume of Settled Material =
1.36 x 109 g/88 g/1 - 1.55 x 10U = 12.5 ac-ft
2. Required Area Based on Storage Area =
12.5 ac-ft/3 ft = 4.2 acres
3. Required Area Based on Ponding =
18.57 cfs x 9,000 sec/(2 ft)(43,560 sq ft/acre) = 1.9 acres
22
-------
FILTRATION DIKE
Filtration Dike Length:
Secondary Effluent Solids Concentration = 30 mg/1
Throughput/sq m = 8 x 104 /M^
Q = 11.5 mgd = 0.5 M^/sec
For 6 Months, Q = (11.5 mgd)(365/2) = 2.1 x 10^ gal
= 7,946,235
For a 6' Top Width and a 10' Height With a 2:1 Slope Area =
(2)(1/2)(10 1)(20 *) + (6 ')(10 *) = 260 SK
= 24.2 M2
Surface Area/LF = (13.4')(1') = 13.4 SF
= 1.2 M2
For Each LF, Throughput =
(8.4 x 10^)(1.2) = 10.5 x 104 —2
L = 7,946,235 M3/10.5 x 104 M3/LF + 76'
23
-------
MIXED MEDIA FILTRATION
Mixed Media Filtration:
Hydraulic Load = 5 gpm/SF
Q = 11.5 mgd
r. c » (11.5 x 106 gpd)/l,440 min ,
Surface Area = fr' . —1 = 1,600 SF
5 gpm/SF
Provide 8 200-SF Units 20' x 10' Cells
24
-------
RUNOFF AND LEACHATE FLOW KATES
The Hydrologic Evaluation of Landfill Performance (HELP) model was run to
estimate runoff and infiltration through the cap (Shroeder, et al., 1983). It
was assumed that all water that infiltrated through the cap would contribute
fully to the leachate production. The area used in the calculations was 80
acres.
Re s u 11 s :
Average Annual Leachate Production
5,086,000 gal
13,900 gpd
25,944,000 gal
71,080 gpd
35.6 inches
13.3 inches
19.9 inches
2.4 inches
Average Flowrate
Average Annual Runoff
Average Flowrate
Average Annual Rainfall
Average Annual Runoff
Average Annual Evaportranspiration
Average Annual Leachate Production
25
-------
ACTIVATED CARBON
Activated Carbon Adsorption:
Q = 11.5 mgd = 19,800 gpm
Hydraulic Load = 5 gpm/SF
Contact Time = 30 min
SA = (19 ,800 gpm)(i|.)/5 gpm/SF = 1 ,650 SF
Use 15 columns, SA = 110 SF/column
D = 12 '
Actual Area = ( ) (122/4) = 113 gp
(113) (15) = 1 ,696 SF
Actual Hydraulic Loading = ( 19 ,800) (-|^-)/1,696 = 3.9 gpm/SF
Bed Depth Required at 30 min Contact Time
V = U9,800 gpm)(30 min)8 = cf/unit
(7.48 gpsf)(20)(24) ' ct/unit
Bed Depth - 1,324/113 = 11.7'
Supply 40% Expansion Room at Top for Backwashing and 3.0 ft for
Freeboard Depth = (0.4)(11.7) + 3.0 + 11.7 = 19.4' (say 20')
Carbon Required = (300 #/mg)(11.5 mgd) = 3,450 #/day
Use 15 - 12' diameter 20* high filters
26
-------
COSTS FOR PROVIDING PLAIN SEDIMENTATION AT A NEARSHORE DISPOSAL SITE
(30-AC POND)
(January 1984 Prices)
Quantity
Unit
Unit Price
Total Cos
Clay Liner 3 Feet Thick
150,000
CY
$18.2 9
$2 ,744 ,000
20 Mil PVC Cap
30
AC
10,000.00
300,000
Earth Cover 2 Feet Thick
112,500
CY
4.001/
450 ,000
Fencing 6 Feet High
Chainlink
2 ,000
LF
6.00
12 ,000
Landscaping Dry Land
Seed ing
30
AC
1,000.00
30,000
Weir Structure
1
JOB
LS
12 ,000
External Dike
1
JOB
LS
925 ,000
Site Development
1
JOB
LS
50 ,000
Subtota 1
$4 ,523 ,000
Contingency + 30%
TOTAL
1 ,357 ,000
$5 ,880 ,000
O&M
OPERATION AND MAINTENANCE COSTS
4 MO $10,000
Contingency + 25%
TOTAL
$40 ,000
10 ,000
$50 ,000
1/Quotation from Commencement Bay.
27
-------
COSTS FOR PROVIDING PLAIN SEDIMENTATION AT AN UPLAND DISPOSAL SITE
(80-AC POND)
(January 1984 Prices)
Quanti ty
Unit
Unit Price
Total Cost
Clay Liner 3 Feet Thick
400,000
CY
$16.29
$6 ,516 ,000
Leachate Underdrain
50,000
LF
4.00
200,000
Granular Bedding
160 ,000
CY
5.00
800 ,000
45 Mil Hypolan Liner
80
AC
35
,000.00
2 ,800,000
Dewatering Drain
50,000
LF
4.00
200 ,000
Excavation/Stockpile
300,000
CY
0.75
225,000
20 Mil PVC Cap
80
AC
10
,000 .00
800 ,000
Earth Cover 2 Feet Thick
From Stockpile
300,000
CY
0.75
225 ,000
Fencing 6-Foot Chainlink
12 ,000
LF
6.00
72 ,000
Landscaping Dryland
Grass Seeding
80
AC
1
,000.00
80,000
Weir Structure
1
JOB
LS
12 ,000
External Dike
1
JOB
LS
480,000
18-Inch 0 Effluent Pipeline
5,000
LF
20.00
100 ,000
Site Development
1
JOB
LS
100,000
Subtotal
$12,610 ,000
Contingency + 25%
3,152 ,500
TOTAL
$15,762 ,500
OPERATION AND MAINTENANCE COSTS
O&M 4 MO $ 10,000 $40,000
Contingency + 25% 10 ,000
TOTAL $50,000
28
-------
CHEMICAL CLARIFICATION COSTS IN ADDITION TO PLAIN SEDIMENTATION
(January 1984 Prices)
Quantity Unit Unit Price Total Cost
Internal Diking
10,000
CY
$4.00
$40,000
Weir Structure and
Discharge Culvert
1
JOB
LS
12 ,000
Polymer Feed System
1
JOB
LS
60 ,000
Mud Pumping System
1
JOB
LS
50,000
Operation Facility
Portable Building 8' x 12'
1
JOB
LS
9 ,000
Sub total
$171,000
Contingency
¦ + 25%
43 ,000
TOTAL
$214 ,000
OPERATION AND MAINTENANCE COSTS
Polymer $65,000
Labor 105,000
Energy 3,000
Maintenance Material 3 ,000
Subtotal $176,000
Contingency + 25% 44 ,000
TOTAL $220,000
29
-------
COSTS FOR PERVIOUS DIKES AT UPLAND AND NEARSHORE DISPOSAL SITES
(January 1984 Prices)
Quantity Unit Unit Price Total Cost
Pervious Dike 10,000 CY $10.00 $100,000
Conventional Dike
Replaced 10,000 CY 4.00 (-) 40,000 savings
Net Cost $60,000
Contingency + 25% 15 ,000
TOTAL $75,000
OPERATION AND MAINTENANCE COSTS
O&M 4 MO $1 ,000 $4,000
Contingency + 25% 1,000
TOTAL $5,000
30
-------
COSTS FOR SANDFILL WEIRS AT UPLAND AND NEARSHORE DISPOSAL SITES
(January 1984 Prices)
Quantity Unit Unit Price Total Cost
Filter Medium 1 JOB LS $29,000
Weir Structure 1 JOB LS 40,000
Subtotal $69,000
Contingency + 25% 17 ,000
TOTAL $86,000
OPERATION AND MAINTENANCE COSTS
Labor $9,000
Materials 4,000
Equipment 3,000
Subtotal $16,000
Contingency + 25% 4,000
TOTAL $20 ,000
31
-------
COSTS OF CHEMICAL PRECIPITATION BY LIME ADDITION FOR
UPLAND AND NEARSHORE DISPOSAL SITES
(January 1984 Prices)
Time Feed Station
Upflow Solids Contact
Clarifier
Sludge Pumping
Quantity Unit Unit Price
1 JOB LS
1 JOB
1 JOB
LS
LS
Subtotal
Contingency + 25%
TOTAL
OPERATION AND MAINTENANCE COSTS
Chemical
Energy
Maintenance Materials
Labor
Subtotal
Contingency + 25%
TOTAL
Total Cost
$145,000
500,000
50,000
$695,000
174,000
$869,000
$340,000
8,000
4,000
19,000
$371,000
93 ,000
$464 ,000
32
-------
ACTIVATED CARBON COLUMNS AT UPLAND OR NEARSHORE DISPOSAL SITES
(January 1984 Prices)
Quantity Unit Unit Price Total Cost
Carbon Columns 15 EA $220 ,000.00 $3 ,300 ,000
Carbon Regeneration 1 JOB LS 700 ,000
Subtotal $4,000,000
Contingency + 25% 1,000 ,000
TOTAL $5 ,000 ,000
OPERATION AND MAINTENANCE COSTS
O&M 4 MO $99,000 $396,000
Contingency 4^ 25% 99 ,000
TOTAL $495 ,000
33
-------
COSTS FOR OZONATION AT UPLAND AND NEARSHORE DISPOSAL SITES
(January 1984 Prices)
Quantity Unit Unit Price Total Cost
Equipment 1 JOB LS $1,280,000
Subtotal $4,000,000
Contingency + 25% 320 ,000
TOTAL $1,600 ,000
OPERATION AND MAINTENANCE COSTS
O&M 4 MO $60,000 $240 ,000
Contingency + 25% 60 ,000
TOTAL $300 ,000
34
-------
lit A <*0 51A
1 ' .aH^TTI !
AREA NUMBER AREA DESIGNATION
1 HYLEBOS WATERWAY
2 8LAIR WATERWAY
3 SITCUM WATERWAY
4 MILWAUKEE WATERWAY
5 ST. PAUL WATERWAY
6 MIDDLE WATERWAY
7 CITY WATERWAY
8 WEST SHORE
9 PUYALLUP RIVER
10 RUSTON
PLATE 1: SITE BOUNDARIES OF
THE COMMENCEMENT BAY
NEARSHORE/TIDEFLATS
SUPERFUND SITE
• x'*;
V
~"ru .'fOftkuM
-------
HYLEB0»O ^
DISPOSAL S1T£»2
HYLE90S BROWNS POINT
DISPOSAL SITE J J
0LAIR GRAVING DOCK
DISPOSAL SITE
PORT OF TACOMA
DISPOSAL SITE "E"
MYLf BOVCR
dis*o»4l Si
BLAIR SUPS
DISPOSAL SITES
BLA. R WATERWAY
OUTER
INNER
PORT OFTACOMA
DISPOSAL SITE D'
MILWAUKEE WAT £RWAY
DISPOSAL SITE ^ .. -
PORT OP TACOMA
DISPOSAL SITE cS'
PUYALLOPRIVO? RAILROAD
DISPOSAL SITE V ...
PUYALLUP RIVER DELTA
DISPOSAL SITE
PUYALLUP
MITIGATION
DISPOSAL SITE
¦midole waterway
DISPOSAL MTE
SCAtE-1 (4 000
POTENTIAL DISPOSAL SITES
iN commencement bay, wa*
PLATE 2:
i
i
-------
LEVEL I
LEVEL II
LEVEL III
LEVEL IV
DREDGE _
INFLUENT
PLAIN
SEDIMENTATION
I
CHEMICAL
CLARIFICATION
FILTRATION
PRECIPITATION
FILTRATION
CARBON
ADSORPTION
OZONATION -1
DISTILLATION
ELECTRO-
DIALYSIS
FINAL
EFFLUENT
REVERSE
OSMOSIS
ION
EXCHANGE
Plate 3: Treatment Processes Flow Diagram for Cost Estimating
-------
REPLY TO
WAT L:HWAYS EXPERIMENT STATION, CORPS Of ENGINEERS
PO BOX 631
VICKSRURG MISSISSIPPI 39100
DEPARTMENT OF THE ARMY
October 26, 1983
ATTENTION OF
Environmental Laboratory
Dr. Keith Phillips
U. S. Army Engineer District,
Seattle
NPSEN-PL-ER
P. 0. Box C-3755
Seattle, Washington 98124
Dear Dr. PJiiWips:
Attached is the classification of Commencement Bay organic
chemicals by solubility which you requested under the Dredging
Operations Technical Support (DOTS) Program. In addition to the
requested classification, the Environmental Laboratory staff is
preparing information on the bioavailability and maximum bioaccum-
ulation potential of these chemicals from Commencement Bay sedi-
ment. This information will be provided within three weeks.
If there are any questions concerning the attached or upcom-
ing information, please contact Mr. Victor McFarland at (601)
634-3721 or FTS 542-3721. Thank you for the opportunity to pro-
vide assistance under the DOTS Program.
Sincerely
Charles C. Calhoun, Jr.
Manager, Environmental
Effects of Dredging Programs
Attachment
-------
A Solubility and Mobility Classification of Organic Chemicals
Identified in Commencement Bay Sediments
Introduction
In this report fifty-six of the organic chemical contaminants most fre-
quently identified in Commencement Bay sediments (Johnson et al., 1983) have
been classified according to their solubilities in water and their relative
mobilities when bound to soil or sediment. This classification identifies
chemicals which may be expected to behave similarly in terms of water solu-
bility and cohesiveness with particulate matter under similar physical
conditions.
The water solubility (S) classes are based on the behavior of the chemi-
cals in pure water at 25°C. Since organic chemicals associate primarily with
the organic carbon fraction of soils and sediments, their mobilities are based
upon soil or sediment organic carbon/water partition coefficients (Koc). Both
S and Koc are linearly correlated with octanol/water partition coeffic-
ients (Kow) which may be obtained from the literature or calculated using
molecular structure techniques. Many of the values of S and Koc listed in
this report are derived from Kow, and the remainder are taken from empirical
determinations in the literature.
Determinations of S using Kow were by the equation of Yalkowsky, et al.,
(1983), which corrects for the effect of melting point on the water solubility
of isomers. An example is the difference in the classifications given to the
isomers anthracene and phenanthrene which fall in different solubility classes
although they are similar in mobility.
Mobility classifications follow the scheme of Swann, et al., (1983), and
calculations of Koc were made using the equation of Karickhoff (1981).
The procedure for inclusion of data is as follows:
-------
Water Solubility (S)
1. If several experimentally obtained values were reported in the literature,
outliers were excluded and the mean of remaining values was used.
2. If values reported in source works were identified as "estimated" they
were not used.
3. If single values were found for a given chemical, the single value was
used if it appeared consistent with estimation results.
4. If no values could be found for S at 25°C, but were found at other temper-
atures the values were extrapolated to 25°C.
5. If no values of S could be found they were estimated using Kow and melting
point; melting points below 25°C were calculated as being 25°C.
Qctanol/Water Partition Coefficient (Kow)
1. Measured values of Kow were treated similarly to measured values of S
(means of several reported observations, outliers excluded).
2. If measured values of Kow were not found, the structure of the chemical
was established and Kow was calculated by the fragment constant methods of
Hansch and Leo (1979).
Mobility (Koc)
1. Reported values of Koc were treated similarly to reported values of S and
Kow. Experimental values were used preferentially, but if not available Koc
was estimated (Karickhoff, 1981).
2
-------
Table No. 1
Factors Relevant to Long-Term Contaminant
Mobility in Soil/Sediment Environments
1. Chemical Species
molecular weight and chemical structure
solubility in water and vapor pressure
diffusivity in water and in pore gas
partition coefficients and Henry's constant
2. Solvents (pore water and pore gas)
molecular weight of water and gas
concentration and partial pressure of other species
3. Soil/Sediment Matrix
porosity (micro, macro)
grain size (average and standard deviation)
permeability (water and gas)
organic fraction and ion-exchange capacity
water content (for soil)
tortousi ty
level and depth of bioturbation
4. Fluid Properties
temperature, pressure and phase (6, L, S)
water flow rate and direction
gas flow rate and direction
5. Total Contaminant Concentration Level
low; < 50,000 ppm (wt)
high >_ 50,000 ppm (wt)
6. Geometric Factors
length of diffusion and convection pathways
cover layer depth
disposal cell dimensions
3
-------
Table 1
Relative Water Solubility Classification for Organic Chemicals
Identified in Commencement Bay Sediments
Rank.
Range,
,-1
mg (
Solubility Class
1
1,000
- 10,000
very high
2
100
- 1000
high
3
10
- 100
med turn
4
0.1
- 10
low
5
0.01
- 0.1
slight
6
0.001
- 0.01
vi'ry slight
7
< 0.001
practically insoluble
Table 2
Classification of Chemical Mobility in Soil*
Rank
Approximate K
oc
Mobility Class
1
0
1
U"!
o
very high
2
50 - 150
high
3
150 - 500
medium
4
500 - 2,000
low
5
2,000 - 5,000
slight
6
>5,000
immobile
* Adapted from: Swann, R. L., et al., in: Residue Reviews, Vol. 85,
Springer-Verlag New York Inc., 1983.
4
-------
Table 3
Classification by Mater Solubility and Soil Mobility of Some Organic
Chemicals Identified in Commencement Bay Sediments
I. Volatile
Solubility
Mobility
1.
chloroethane
(1)
(1)
2.
1, 1-dichlorethane
(1)
(1)
3.
1, 1-dichloroethylene
(1)
(1)
4.
1, 2-dichloroethane
(1)
(2)
5.
trichlororoethane (chloroform)
(1)
(2)
6.
1, 1, 1-trichloroethane
(1)
(2)
7.
benzene
(1)
(2)
8.
bromoform
(1)
(2)
9.
carbon tetrachloride
(1)
(3)
10
1, 1, 2, 2-tetrachloroethane
(1)
(3)
11
1, 2, (trans) dichloroethylene
(2)
(1)
12.
toluene
(2)
(3)
13.
tetrachloroethylene
(2)
(3)
II. Base/Neutral
1.
nitrobenzene
(1)
(1)
2.
dimethyl phthalate
(2)
(3)
3.
1, 2-dichlorobenzene
(2)
(4)
4.
1, 3-dichlorobenzene
(2)
(4)
5.
1, 4-dichlorobenzene
(3)
(4)
6.
naphthalene
(3)
(4)
7.
2-chloronaphthalene
(3)
(5)
8.
diethyl phthalate
(3)
(6)
9.
bis (2-ethylhexyl) phthalate
(4)
*
10.
di-n-octyl phthalate
(4)
*
11.
hexachlorobutadiene
(4)
(4)
12.
fluorene
(4)
(5)
13.
acenaphthylene
(4)
(5)
14.
acenaphthene
(4)
(5)
(Continued)
* Mobility not estimated
5
-------
Table 3 (Concluded)
II.
Base/Neutral
Solub ility
Mobility
15.
hexachloroetharie
(4)
(6)
16.
phenanthrene
(4)
(6)
17.
fluoranthene
(4)
(6)
18.
butylbenzyl phthalate
(4)
(6)
19.
pyrene
(4)
(6)
20.
di-n-butyl phthalate
(4)
(6)
21.
benzo (a) anthracene
(4)
(6)
22.
ideno (1, 2, 3-cd) pyrene
(5)
(6)
23.
anthracene
(5)
(6)
24.
chrysene
(6)
(6)
25.
hexachlorobenzene
(6)
(6)
26.
benzo (b) fluoranthene
(6)
(6)
27.
benzo (a) pyrene
(6)
(6)
28.
benzo (k) fluoranthene
(6)
(6)
29.
benzo (g, h, i) perylene
(7)
(6)
III.
Acid
Extractable
1.
phenol
(1)
(1)
2.
p-chloro-m-cresol
(1)
(1)
3.
4-nitrophenol
(2)
(1)
A.
2-chlorophenol
(2)
(2)
5.
2, 4, 6-trichlorophenol
(3)
(5)
6.
pentachlorophenol
(4)
(6)
IV.
Pesticides and PCB's
1.
aldrin
(2)
(3)
2.
lindane (*y-BHC)
(3)
(5)
3.
4, 4' - DDD
(4)
(6)
4.
PCB - 1242, 1016
(4)
(6)
5.
4, 4' - DDE
(5)
(6)
6.
PCB - 1248
(5)
(6)
7.
PCB - 1260
(5)
(6)
8.
4, 4' - DDT
(6)
(6)
6
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Sources and References
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8
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