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Introduction to Sediment Remediation
Presented to:
Lower Passaic River Community Advisory Group
July 14, 2011
Overview
Feasibility Considerations
• Conceptual Site Model
• Dredging / Capping
• Dredged Material Management
Design
Construction
The Practice of Contaminated Sediment
Management
RemediationRisk, Inventory
Restoration
Habitat, Water Quality
NavigationDepth, Width
Some Important References
http://www.epa.gov/superfund/health/conmedia/sediment/guidance.htm
http://el.erdc.usace.army.mil/elpubs/pdf/trel08-4.pdf
Interpreting the Conceptual Site Model
Areas of High Concentration
Areas of High Inventory (Mass)
Sediment Stability Considerations
Receptor Pathways
A Simplified Look at the Sediment
Water Column Solids Transport
Bed Load Transport
Biologically Active Zone
Bioavailable Zone
Erosion / Deposition,
Biological Uptake
Buried Contaminated Sediments
Porewater flux,
Contaminant
degradation
Native Geologic Materials Groundwater
discharge
ZONESOME CONTAMINANT
TRANSPORT PROCESSES
SEDIMENT TRANSPORT
Sediment StabilitySome ways to assess sediment stability include:
Determine Bathymetric Changes
Evaluate Sediment Texture
Understand Geomorphology
Estimate Storm Event Velocities
Perform SedFlume or Gust Microcosm Experiments
Perform Sediment Transport Modeling
Some Key Topics for Remedy Selection
Where to Remediate: Active vs. Monitored
Natural Recovery
What method: Dredging vs. Capping (vs. Insitu)
How to Manage the Sediments
Effectiveness & Recontamination
Other Site-Specific Factors
NEEDS
GOOD PREDICTIVE MODEL
COMMON SENSE
STAKEHOLDER INPUT
DREDGING
DREDGING:
Feasibility & Design
Considerations & Terminology
Resuspension
Residuals
Dredged Material
Management
Productivity
Dredge Prism
Debris / Utilities / Structures
Dredging Technology
Delivery Techniques
Navigation
Slope Stability
Productivity
Contracting Approach
Dredging Advantages/Limitations
(per USEPA Guidance)
* Where cleanup levels achieved
Advantages
Lower uncertainty for long-term
effectiveness*
More flexibility for future use
Less reliance on institutional
controls
Less time to achieve goals than
Monitored Natural Recovery
Allows for treatment/beneficial
use of sediments
Limitations
More logistically complex and
costly
Treatment technologies still in
scale-up mode; may be costly
Disposal facilities / options may
be limited
Difficulty in estimating residual
contamination
Effects of resuspension and/or
volatilization
Temporary disruption of aquatic
community and habitat
Some Dredging Resuspension
Terminology (General Illustration)
Minimizing Sediment Resuspension
Equipment Selection
Operator Experience
Best Management Practices (BMPs)
Containment (Curtains, Barriers, Sheetpile)
Innovative Approaches
Source: Bean Environmental, Cable Arm
Dredging Equipment SelectionHorizontal Profiler
Horizontal Auger (MudCat)
Cutterhead
CableArm
Some Best Management Practices for
Resuspension
Monitoring
Bucket Closure Sensors
Lift Speed Control
Equilibration Time
Rinse Tank / Clean Bucket
Minimize Equipment Moves
Penetration Depth
Emerging Technologies for
Resuspension Control
Control Zone
Insitu Stabilization
Resuspension TrendsR
ES
US
PE
NS
ION
DREDGE PRODUCTION
MASS
RATE
FRACTION OF
MASS REMOVED
NORMAL OPERATING RANGE
Navigation Sources of Resuspension
Photo provided by PANYNJ.
Contaminated Sediments
“Clean” Over-cut Sediments
Residual Sediments
Dredge
Pre-dredging
Elevation
Of River Bottom
Overdredge Depth
Design Cut Line
Sampling of
Residuals
DREDGING RESIDUALS
Residuals Tidbits
Prediction: The concentration of contaminants in dredging residuals is an integration of the concentration of the last bucket dredged.
Reynolds Metals Case Study: After each dredging pass, approximately half of the dredge certification units (cells) met the cleanup criteria. One cell was dredged 13 times.
Operator skill appears to be one of the keys to reducing residuals.
Backfill can be effective used to attenuate residuals.
Managing Dredging Residuals
Good Inventory Characterization & Dredge to
Defined Elevation with backfill
Redredging
Specialty Equipment
Backfilling (Dilution)
Capping
Dredged Material Management
Disposal
CAD Cells
CDFs
Placement Sites
(Brownfields)
Decontamination
Waste Management
Facilities (Landfills)
Handling
Delivery: Barge vs. Hydraulic
Dewatering vs. Desiccation
Water Treatment
Transport: Barge vs. Rail vs.
Truck
Dredged Material Management Options
Decontamination Technologies
Minergy Biogenesis Endesco / GTI (now Volcano) Upcycle Source: http://www.state.nj.us/transportation/works/maritime
Bean Environmental Bonacavor
Hydraulic Excavator Dredge
Dredging Scow Transport Hydraulic Offloading
Off-site Disposal or
Beneficial Use
http://www.foxrivercleanup.com/foxrivercleanup/photo+gallery/default.asp
http://www.dfo-mpo.gc.ca/regions/central/pub/fact-fait-mb/mb1_e.htm
Courtesy of John Henningson; Henningson Environmental Services, Inc.
Putting it All Together
http://www.foxrivercleanup.com/foxrivercleanup/photo+gallery/default.asp
Water Treatment Plant
Stockpile for Treatment /
DisposalDewatering
CAPPING
Capping Feasibility & Design
Considerations & Terminology
Thickness
Grain Size
Filter Design
Maintenance
Borrow Source Identification
Reactive Layers
Physical Barriers
Performance criteria
Pre-dredging
Habitat Layers
Cap Stability - Erosion
Cap Structure
Navigation
Porewater Fluxes
Flooding Impacts
Capping Advantages/Limitations
(per USEPA Guidance)
Advantages
Quickly reduce exposures
Clean substrate for benthic re-colonization
May enhance habitat
Less infrastructure for material handling
Less potential for resuspension
Avoids risks associated with material
treatment or disposal
Usually lower cost and less disruption
than dredging and sediment
treatment/disposal
Limitations
Contaminated sediment remains –
could be released if disturbed or
break through
Possibility of sediment disruption
during placement
Shallow water may require
inconvenient institutional controls
(e.g., boating restrictions)
Cap may alter hydrologic regime
Cap materials may alter biological
community
Long-term monitoring and
maintenance
Placement Techniques
Hydraulic Diffuser
Conveyor
Split-Hull BargeClamshell
Source: Bean Environmental
Cap Placement Equipment - Spreader
Examples of Completed Capping
Projects (Year Completed)
St. Paul Waterway, WA (1991)*
Marathon Battery, NY (1994)
Eagle Harbor, WA (2002)
Grasse River, NY (2005) – pilot study
Anacostia River, MD (2007) – pilot studies
Fox River, WI (ongoing)
*part of the Commencement Bay - Nearshore Tideflats Superfund Site
which consists of 8 contaminated sediment problem areas within 6
marine waterways.
Implementation / Construction Issues
Processing Facility Siting
Contractor Selection
Operator Experience
Management / Oversight
Community Involvement
Change Management
QUESTIONS ?