Contaminated Sediment Sites –
The Evolution of In-Situ Capping
as an Effective Remedial Technology
IX International Seminar on
Remediation and Redevelopment of
Contaminated Sites
2 October 2014
Overview
• Sediment Remediation Utilizing Capping
• Types of Capping Technologies
• Recent Advancements in Capping Technology
• Cap Placement Delivery Systems
Introduction
The USEPA generally recognizes three major approaches
for sediment remediation:
• Monitored Natural Recovery (MNR)
• In-situ Capping
• Dredging, with Treatment and/or Disposal
The preferred remedy at large complex sites is often a
combination of alternatives as each approach has its
limitations. In-situ treatments have the potential for
increased effectiveness and significantly reduced costs over
conventional approaches.
Why are We Interested
in “In Situ” Capping?
• Recent advancements in
capping technology
• Immediate risk reduction
• Can be less expensive
than dredging
• Minimal resuspension of
contaminated sediment
• Can take less time to
implement than other
remedies
Courtesylok®
Armor Layer
Active or Passive Cap Layer
Contaminated Sediments
Benthic Layer
2000 – Present Active Caps
Example Sites:
2002 - AC, Olympic View Resource Area, WA
2003 - Coke in RCM, Apatite, Anacostia River
2006 - AC in RCM, St. Louis River, Duluth, MN
2011 – OC, Roxana Marsh, Grand Calumet, IN
2012 – AC (bulk placement), Onondaga Lake, NY
2013 – SediMiteTM (bulk placement), Mirror Lake, Dover, DE
Late 1990s Barrier Caps
Example Sites:
1999 – Clay based composite, Ottawa River, OH
1999 – Geosynthetic clay liner Little Elk Creek, MD
Late 1970s Sand / Silt and Reuse of Navigation Dredge Material
Example Site:
1978 – Sand, Stamford-New Haven, CT
In Situ Capping Innovations
Key:
AC = Activated Carbon
OC = Oleophilic Clay
RCM = Reactive Core Mat
Selection Considerations for
In Situ Capping
In Situ Capping
• Site Conditions
• Remediation Goals
• Long-Term Effectiveness
• Implementability
• Cost Effectiveness
• Sustainability
• Physical Environment
• Low Energy Environment
• Erosion Potential
• Hydrodynamic and Geotechnical Conditions
• Gas Ebullition
• Thickness of Cap
• Present and Future Use
• Source Control
Site Evaluation
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Contaminant Transport Mechanisms
Between Contaminated Sediment and Cap
• Flux – advection (groundwater upwelling)
• Flux – diffusion (concentration gradient)
• Bioturbation
• Gas Ebullition
Gas Ebullition
Cap Design
Sequence
Determine if Capping
is Appropriate for Site
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Cap Design
Sequence
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• Cap Material
• Bioturbation Component
• Consolidation Component
• Erosion Component
• Operational Component
(Cap Integrity)
• Chemical Isolation
Advantages
− Often more cost effective than removal
− Immediately reduces exposure to contaminants
− Significantly lower resuspension during implementation
− Can be shorter construction duration
Limitations
− Does not remove contamination
− Generally requires long-term monitoring and maintenance
− Often more difficult to get regulatory approval
Sediment Capping
Comparison to Dredging
Summary of Sediment
Capping Technologies
Sediment Capping
Technologies
• Conventional Capping
– Clean Sand / Sediment
• Active Capping (contaminant)
– Carbon (organics, mercury)
– Oleophilic Clay (NAPL, oils)
– Apatite / Zeolite (metals)
– Zero-Valent Iron
– Microbial Activity Enhancement
• Low cost in-situ
remediation option
• Physical isolation
• Critical factor – cap
installation
• Reduce contaminants
transfer rate
• Immobilization of
contaminant - small
Conventional Sand Cap
Contaminated
Sediment
Sand Cap
Overlying Water
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Cap Amendment Delivery Systems
Permeable Active Layer
AquaGate+PAC®
• Composite aggregate,
delivery of carbon (and other
active materials)
• Chemically sorptive
permeable layer
• Can be applied using
clamshell, broadcasting, or
conveyer
Contaminated
Sediment
SediMiteTM
Granule Layer Placement
Overlying Water
Contaminated
Sediment
Granule Breakdown
Intermixing / Bioturbation
Overlying Water Courtesy of AquaBlok®
SediMiteTM
• Minimal destruction of the existing habitat
• Mixes into the benthic layer through natural
sediment mixing processes
• Generally applied using broadcasting
• Composite aggregate barrier technology
• AquaBlok® material swells up when hydrated
• Impermeable chemically sorptive barrier
Cap Amendment Delivery Systems
AquaBlok® Cap
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Cap Amendment Delivery Systems
Reactive Core Mat® (RCM)
Supplier:
• Commercially available
• Permeable reactive cap
• Incorporate variety of media to target
specific contaminants
• Reduction in contaminant transport
• Reduced cap thickness
Courtesy of InterGEO Services
Innovative Capping Techniques
Three innovative in-situ capping technologies
developed (and utilized by);
• Sevenson Environmental Services, Inc., 2749
Lockport Road Niagara Falls, NY 14305 USA
• J.F. Brennan Co., Inc., 820 Bainbridge Street,
LaCrosse, WI 54603 USA
• Great Lakes Dock and Dredge Corporation,
2122 York Road, Oakbrook, IL 60523 USA
Water Based – BCS™
• Minimal Mixing
– Less than 1”
• Undisturbed Soft
Sediment
– Reduced velocity
placement
• Increase Accuracy
• Save Significant
Volume of Cap
Material
Capping Results
Obrigado!
George L. Hicks
Global Practice Director
Sediment Management & Remediation
CH2M HILL
Chicago, Illinois, USA