Contaminated Sediment Management Still an Oxymoron

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Contaminated Sediment ManagementStill an
Oxymoron?
Danny Reible Chevron Professor of Chemical
Engineering Director, Hazardous Substance
Research Center/SSW Louisiana State
University Baton Rouge, LA 70810
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Outline

• Contaminated Sediments - What makes them so
  difficult?
• How did we manage sediments in 1985-1990?
• How do we do it now?
• What do we know about contaminated sediment
  processes?
• - Dynamic sediment environments
• - Stable sediment environments
• - Bioavailability/bioaccumulation of
  contaminants
• So what are the options?
• Contaminated Sediment Management - Still an
  Oxymoron?

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Hazardous Substance Research Center
South and Southwest

• Established under CERCLA
• Mission
• Research and technology transfer
• Contaminated sediments and dredged material
• Unique regional (46) hazardous substance
  problems
• Contact info - Danny D. Reible, Louisiana State
  University
• Ph 225-388- 6770
• Email reible_at_che.lsu.edu
• Web www.hsrc.org

LSU
Georgia Tech
Rice
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Research Theme Areas for HSRC/SSW
Contaminant availability in sediments ltIts not
what we can measure, its what can receptors
absorb? Biotransformation processes of
contaminants in sediments ltIs recovery possible
without the risk/expense of physicochemical
treatment? Science of risk management for
sediments ltHow do we select and design
appropriate technologies? Unique regional
hazardous substance issues ltAre there regional
problems that have been overlooked in the
national debate?
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Key Research Contributions To-Date
HSRC/SSW
Availability ltDeveloped promising approach to
evaluate availability of nonpolar
organics ltIdentified limitations of SEM/AVS ratio
to define metals availability ltIdentified
importance of volatile release from
sediment/dredged materials Biotransformation ltId
entified mechanism and limitations of
phytoremediation of TNT ltDeveloped a simple and
inexpensive sediment biodegradation
technology ltObserved enhanced PAH degradation by
common benthic organisms Science of risk
management ltHelped develop contaminant loss
criteria for technology selection ltDefined a
robust and relatively inexpensive in situ
monitoring technology ltDeveloped design guidance
for in-situ and dredged material capping
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Contaminated Sediments
What makes them so difficult?
Reside in highly variable, dynamic
systems ltNormal variation in flows and storm
events ltSignificant source of uncertainty
Large volume of sediment ltOften greater than 1MM
m3 ltAverage Superfund site involving ex situ
treatment - lt30,000 m3 Large amounts of
water ltHydraulic dredging generates at least 4
volumes water per volume sediment ltControls on
environmental dredging often causing average
solids content of dredged material to be 1-10
Often marginal contamination with incomplete
exposure pathways and uncertain risks to human
and ecological health
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Contaminated Sediments
What makes them so important?
Historical sources of contamination largely
controlled ltLeaves legacy of contaminated
sediments as important source ltContinuing
sources, however, limit potential cleanup Lack
of disposal options is a major impediment to
harbor development lt95 of shipping trade passes
through dredged ports Significant impediment to
unrestricted usage of waterways ltFish advisories
throughout Great Lakes and other areas
Widespread problem lt Of 21,000 national sediment
sampling stations (1996 Survey) 26 exhibit
potential of adverse effects Additional 49
exhibiting intermediate probability of adverse
effects lt About 30 of Superfund sites involve
contaminated sediments
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How did we manage sediments?
1985-1990
Assumed ex situ technological solutions
available ltRemoval via dredging ltTreatment or
disposal onshore Deferral of large, complicated
sites ltHudson River ltNew Bedford Harbor ltFox
River Attempts to implement conceptual approach
at Asmall_at_ sites lt Bayou Bonfouca, Louisiana
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Bayou Bonfouca
Facility ltWood treating facility in operation
since 1892 ltEmployed and released
creosote ltAdjacent to navigable bayou -
Bonfouca Bayou Bonfouca lt150,000 - 170,000 cu
yd of contaminated sediments ltSurficial
concentrations to 13,450 mg/kg total PAHs
Remediation ltRemoval of sediments in excess of
1300 mg/kg - mechanical excavator ltIncineration
of dredged material and burial of incinerator
residual ltCapping of residual contaminated
sediments in bayou ltTotal Cost - 130 million
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How do we manage sediments now?
Increased reliance on predictive modeling of
options ltNeed to understand natural fate and
transport processes ltNeed to understand normal
and episodic hydraulic state ltEvaluation of
management options requires sophisticated
prognostic models Increased reliance on in situ
options ltMonitored natural recovery ltIn-situ
capping ltBioremediation and/or stabilization
Large, complicated sites still unresolved
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Contaminated Sediments
What are the Options?
Natural Recovery Passive In-Situ Treatment
or Containment Removal and Upland Treatment or
Containment Removal and Subaqueous Treatment
or Containment
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How do we choose among the options?
Ultimate Goal - Reduction of Risk ltReduction or
elimination of exposure and exposure
pathways ltComplications BHuman Risk - Selection
and quantification of exposure pathways/effects? B
Ecological Risk - Pathways? Exposed Species?
Effects? ltSurrogate measures often used instead
Surrogate Goal - Mass Removal ltReduction in
whole sediment concentration ltCommonly used and
just as commonly misses the mark! Alternative
Goals ltReduction in surface sediment
concentration ltReduction in fish tissue
levels ltReduction in water column
levels ltReduction in integrated
concentration/exposure/risk
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Natural Recovery of Contaminated Sediments
When is it appropriate? ltLarge volumes of
contaminated sediment with marginal level of
contamination ltLow energy, depositional
environments ltDredging for navigation not
required ltNot a do-nothing proposition- entails
monitoring and institutional controls ltNot an
ineffective approach chosen to minimize costs -
may be best approach Example - Kepone in James
River ltExpected to eliminate fish advisories
faster than active remedial alternatives ltModel
employed to assess recovery ltRecovery met targets
- James River considered remediated What are
possible enhancements? ltSediment traps to enhance
deposition ltParticle broadcasting - artificially
enhanced deposition ltSource area removal -
outfalls and sediment hot spots
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Passive In-Situ Containment or Treatment
What is it? ltEnhanced biodegradation ltIn-situ
solidification ltContainment - capping When is
it appropriate? ltWhen removal may result in
unacceptable or increased risks ltWhen hydraulic
and other water body conditions are
supportive ltWhen navigation dredging is not
required What are the key assessment
needs? ltEvaluation of effectiveness/engineering
feasibility of approach ltEvaluation of long-term
contaminant fate ltEvaluation of armoring needed
to maintain stability of sediments during
treatment Capping ltMay be used alone as
containment or in combination with in-situ
treatment to ensure containment during treatment
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In-Situ Treatment Options
Enhance containment (capping) to provide time
for treatment PEnhance natural adsorption and
sequestration processes ltAddition of
adsorbents ltPermeability controls ltEnhance
deposition to ensure clean surficial sediments
Enhance natural fate processes ltAddition of
reactants/catalysts BFerrous sulfate or iron
addition for anaerobic degradation of chlorinated
organics BOxygen sources for aerobic
degradation ltCapping to drive anaerobic
conditions and (often) mobility reduction for
metals Active in-situ treatment ltIn-situ
solidification technologies ltIn-situ reactor
(e.g. auger/reactive hood technologies)
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Removal with Upland Treatment and Containment
What is it? ltHydraulic or mechanical
dredging ltGenerally requires temporary holding
facility -confined disposal facility
(CDF) ltUpland landfill or treatment/destruction
in incinerator, thermal desorber, biotreater,
etc When is it appropriate? ltDredging required
for navigation purposes ltDredging will not result
in unacceptable or increased risks ltDredging can
be accomplished with minimal generation of
contaminated water ltUpland treatment and
containment options available and
cost-effective What are the key assessment
needs? ltEvaluation of contaminant losses during
dredging and handling ltEvaluation of ecological
effects of sediment removal ltEvaluation of solids
content of produced dredged material
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Environmental Dredging
A Double-Edged Sword?
Limited removal efficiency ltMultiple passes,
overbite generally required to meet removal
targets ltRemoval hindered by debris or presence
of bedrock or hardpan Large quantities of
potentially contaminated water generated ltEnvironm
ental dredging conditions tends to increase
produced water ltMost environmental dredging
operations achieve less than 10 solids
produced Contaminant losses during
operation ltSilt curtains limit impact of
resuspended sediment, minimal impact on released
contaminants ltEfforts to reduce contaminant
losses at point of dredging tend to slow
operations and increase volumes of water
produced ltLosses to air, water from holding cell
(confined disposal facility)
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Dredging - A Double-Edged Sword
Example of Exposure of Buried Contaminants
PBulk of mass initially buried PDredging removes
upper layers and significant contaminant
mass ltSediment removed to layer 3 ltTotal removal
75 of contaminant PResult - Exposure
doubled! ltConcentration in surficial sediments
BPre-dredging (layer 1) , C10 BPost-dredging
(layer 3), C20 PCommon observation lthistorical
contamination depositional environment ltsufficient
overbite impossible/undesirable
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Navigational Dredging

• Non-dredging options essentially unavailable
• Operational changes to allow non-removal options
  shouldnt be be overlooked
• Because of lack of viable options, non-removal
  often default
• Forced to consider upland treatment or
  containment
• Return to subaqueous environment remains an
  option
• Level -bottom capping
• Return of contaminated dredged material to
  subaqueous environment
• Capping with clean sediment
• Confined aquatic disposal
• Preparation of subaqueous pit
• Return of contaminated dredged material to
  subaqueous pit
• Capping with clean sediment

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When are Natural Processes Important?

• When natural recovery is the preferred option
• When removal approaches leave a residual
• When secondary areas of contamination are not
  actively remediated
• When upland treatment and disposal options leave
  a residual
• Conclusion
• Natural Recovery is a component of ALL sediment
  remediation options

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Pathways of Water-Column Exposure via Natural
Processes
Direct exposure due to resuspension of bottom
sediment ltRiverine systems and shallow water
environments subject to storms ltWater column
tends to equilibrate with resuspended
sediment ltAt sufficiently high sediment loads,
water column approaches equilibration with bed
sediment levels ltAnalogous to exposure during
dredging events Indirect exposure by
contaminants moving into food chain ltContact of
benthic organisms to contaminated sediment
followed by predation by higher animals ltBenthic
organisms tend to equilibrate with the bed
sediment ltBasis for sediment quality criteria
Direct exposure due to contaminant release from
stable sediments ltVariety of natural processes
result in contaminant migration to overlying
water ltDegree of equilibration of overlying water
dependent upon rate of these processes Natural
recovery in-situ remediation requires
assessment / intervention to control these
natural pathways
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Contaminant Processes at the Sediment-Water
Interface
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Important Natural Processes
Diffusion ltUbiquitous but generally slow for
sediment-associated contaminants
Advection ltDefined by local groundwater
gradients ltIn permeable beds also influenced by
local pressure variations due to flow over uneven
sediment bed ltAlso slowed by sorption to
sediment Sediment resuspension and
deposition ltResuspension and scouring potentially
dominate mechanism of movement of
sediment-associated contaminants ltDeposition
enhances containment and natural recovery of
surficial sediments Bioturbation ltSignificant
sediment reworking due to presence of benthic
organisms ltTends to be most significant process
for sediment-associated contaminants in stable
sediments
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Table
C-1
Sediment Processes their Relationship to
Sediment Environments
Environment
Environmental Characteristics
Key Fate and Transport Processes
Lacustrine
Low energy environment
Sediment deposition
Generally depositional environment
Water-side mass transfer limitations
Groundwater interaction decreasing away
Groundwater
advection in near-shore area
from shore
Bioturbation (especially in near-shore area)
Organic matter decreasing with distance
Diffusion in quiescent settings
from shore
Metal sequestration
Often fine-grained sediment
Aerobic and anaerobic
biotransformation of
COCs
Biotransformation of organic matter (e.g., gas
formation)
Riverine
Low to high energy environment
Local and generalized groundwater
advection
Depositional or
erosional environment
Sediment deposition and
resuspension
Potential for significant groundwater
Aerobic
biotransformation processes in
surficial
interaction
sediments (potentially anaerobic at depth)
Variable sediment characteristics (fine to
Bioturbation
coarse grained)
Estuarine
Generally low energy environment
Bioturbation
Generally depositional environment
Sediment deposition
Generally fine-grained sediment
Water-side mass transfer limitations
Aerobic and anaerobic
biotransformation of
COCs
Biotransformation of organic matter (e.g., gas
formation)
Relatively high energy environment,
Bioturbation
Coastal Marine
decreasing with depth and distance
Sediment erosion and deposition
from shore
Localized
advection processes
Often coarse sediments
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Characterizing Natural Processes

• Measurements
• Physical, chemical and biological
  characterization of sediments
• Vertical profiles of contaminants or tracers -
  average and episodic behavior
• Monitoring of tracers to indicate source of
  suspended sediment during storm events
• Comparison of contaminant fluxes from sediment to
  flux downriver
• Modeling
• Conceptual and/or mathematical modeling of
  sediment/contaminant dynamics
• Mass flows- tool for comparative assessment of
  potential exposure
• Excellent tool for examining uncertainty or
  spatial or temporal variability

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Dynamic Sediment Environments
Contaminant dynamics often defined by sediment
dynamics ltContaminants strongly associated with
fine particulate fraction ltContaminated areas
generally net depositional environment ltSediments
may still be subject to episodic erosional
events Response of cohesive sediments to high
flow events? Research ltHSRC/SSW
Fundamentals of adhesion of clay particles
(Amirtharajah and Sturm, GIT) Response of
shallow estuarine sediments to storm events
(Ferrel and Adams, LSU) lt Wilbert Lick, UCSB
Developed experimental protocol and modeling
framework currently in wide use
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Significant Natural Processes Influencing
Contaminant Fate
Dynamic Sediment Environment

• Sediment resuspension and erosion
• Sediment deposition
• Sediment suspended load transport
• Sediment bed load transport
• Analogous to resuspension and sediment transport
  during dredging operations
• Exposure defined by equilibrium with resuspended
  sediment

W
C
s
S



C
w




1
K
C
sw
S
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Sediment Movement in Dynamic Environment
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Stable Sediment Environments
Associated with low flow environments
Contaminant dynamics controlled by ltWater side
mass transfer resistances ltSorption retarded
diffusion/advection in pore water ltBioturbation -
normal life cycle activities of benthic
organisms ltContaminant availability
Bioturbation ltDominated by deposit feeders that
ingest sediment ltIncreases sediment cycling to
the surface- surface release of
contaminants ltIncreases porewater irrigation of
sediments ltIncreases oxygen transport into the
sediments- enhancing biodegradation ltOrganism
uptake contributes to transmission up food
chain lt90 of measurements worldwide show
biologically mixed zone lt15 cm
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Bioturbation Enhanced Flux
Bioturbation

M-
T
Coeff
.
Sediment
Age
W
Pyrene
days
mg/kg
Limnodrilus
Lumbriculus
2
26,700 /cm
26,700 /cm
2
2
0.48 mg/cm
1.27 mg/cm
2
0.42
Bayou
30
749
0.46
Manchac
65
60
6
0.290.13
0.350.06
University
30
683
0.41
0.39
Lake
60
596
0.370.12
0.260.06
34
100
80
60
Worm
Control
Moisture Content ()
40
20
0
0
1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
Depth (mm)
35
70
60
50
40
Worm
Control
Pyrene (mg/kg dry)
30
20
10
0
0
1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
Depth (mm)
36
Control Cells
5
Flux
Degradation
43
Remaining
52
Worm Cells
Flux
13
Remaining
15
Degradation
72
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Table C-2
Summary of Characteristic Times of Sediment Fate
and Transport Processes
Process
Characteristic Time
Typical Range of Key
Illustrative Value of
Relationship
Parameter Values
Characteristic Time
1
Diffusion
R
gt 1,000
1,280 years

4
2
R
H
f
f




(Hydrophobic
organics)
t
diff
2
D
p
D
10
cm
/s
-6
2
eff
eff
Advection
Groundwater velocity,
v
,
100 years

H
R
f



t
widely variable
adv
v
Sediment Erosion
Bed erosion rate, U,
10 years
H



t
widely variable
ero
U
Bioturbation
0.3 cm
/yrltD
lt30
13 years
2
2
4
H
bio




t
cm
/yr
2
bio
2
D
p
bio
Reaction
Reaction rate,
k
,
1
100 years
rxn



t
widely variable
fate
k
rxn

Assumes a 10 cm thick
surficial layer contaminated with a hydrophobic
organic with an effective
retardation factor of 1,000. A groundwater
velocity of
1 meter/
yr, a bed erosion rate of 1 cm/
yr, an effective
2
-1
bioturbation diffusion coefficient of 3 cm
/yr and a reaction rate of 0.01 yr
are assumed for purposes of
illustration.
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Contaminant Availability

• Metals availability
• Some success with AVS/SEM ratio
• gt 1 indicates several important metals fixed in
  sulfide form and unavailable
• lt 1 not a clear indicator
• Full description requires sophisticated metal
  speciation dynamics
• Hydrophobic organic availability
• Significant limitations shown for PAHs in soils
  (e.g. Martin Alexander)
• Significant sequestration in sediments containing
  soots
• Biphasic desorption rates and equilibrium
  commonly observed
• Linear, reversible compartment
• Nonlinear, desorption resistant compartment
  (Langmuir in shape)
• Biological Availability?
• Accessibility - Within biologically active zone?
• Availability - Sequestered or available to
  porewater?
• Assimilative Capacity - Can uptake occur?

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r2 0.9
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Summary

• Selection of remedial options should be based on
  risk, not aribtrary and simplistic measures such
  as contaminant mass
• Exposure requires
• Access
• Availability
• Assimilation capacity
• All remedial options entail exposure and risk
• Exposure and risks occur on different time scales
  and magnitudes
• Detailed assessment of each option required for
  valid comparison
• All remedial options have conditions under which
  they are appropriate
• Removal of contaminated sediments from subaqueous
  environment potentially costly and often not the
  best means of reducing risk
• Even dredged material may be best returned to
  subaqueous environment and capped to isolate from
  environment

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What has research contributed?
Improved understanding of sediment fate and
transport processes ltNatural recovery/attenuation
processes ltRecovery of residuals remaining after
active remediation ltRecognition of fundamental
stability of many contaminated sediments
Improved understanding of contaminant loss
processes during application of remedial
options ltIn situ options such as capping ltEx situ
options involving dredging, pretreatment and
ultimate treatment or disposal Development of
in-situ containment and remediation
options ltIn-situ bioremediation ltIn-situ
capping Limited development of technological
options for ex situ treatment and disposal
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Contaminated Sediment Management
Still an Oxymoron?
Improved understanding of what can and cannot
be done Increased reliance on quantitative
tools for assessment and evaluation Use of
these tools growing but conflicts at major sites
remain