Lessons being Learned from the Anacostia Active Capping Demonstration

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Lessons being Learned from the Anacostia Active
Capping Demonstration

• Danny Reible, W. David Constant

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EPA Hazardous Substance Research Center
South and Southwest
Louisiana State University Georgia Institute of
Technology Rice University Texas AM
University University of Texas www.hsrc-ssw.org

• Research and Technology Transfer
• Contaminated sediments and dredged material
• Primarily focused on in-situ processes and risk
  management
• Unique regional (46) hazardous substance
  problems
• Outreach
• Primarily regional in scope
• Driven by community interests and problems
• Sediment Resource Center Member
  http//www.epa.gov/superfund/resources/sediment

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Project Schedule

• 2002/2003 Laboratory evaluation of proposed
  caps
• 2003 Site characterization
• March-April 2004 Placement of active caps
• May 2004 One month sampling event
• September/October 2004 6 month sampling
• September/October 2005 18 month sampling
• September/October 2006 30 month sampling

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Selected Active Caps and Goals of Field Program

• AquaBlokTM w/EPA SITE program
• Evaluate tidal seepage control
• Evaluate potential for uplift during tidal range
• Coke
• Evaluate PAH sequestration/retardation
• Evaluate placement in laminated mat designed and
  built by CETCO
• Apatite
• Evaluate metal sequestration/retardation
• Evaluate effectiveness of direct placement
• Sand (for comparison)

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Site Field Assessment

• Relatively homogeneous sediment properties and
  contaminant distribution
• Steady depositional environment
• Shallow zone of bioturbation reworking
• Tidally influenced seepage near shore
• Significant gas generation and release

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Anacostia Geochronology from Radionuclide Profiles
Pb-210, Cs-137 profiles suggest deposition 0.44
0.84 cm/yr Be-7 profiles suggest 4 cm
accessible layer and bioturbation mass transfer
coefficient of 6-9 cm/yr
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Cap Placement

• Can conventional equipment (clamshell) be used to
  place a relatively thin, uniform layer using the
  innovative capping materials?
• Targets
• 6 inches of apatite with 6 inches of sand
• 4 inches of Aquablok with 6 inches of sand
• 1 inch of Coke (laminated mat) with 6 inches of
  sand
• 12 inches of sand in two lifts

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Sand/Apatite
AquaBlok
Coke Breeze
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Mat Placement
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Cap Thicknesses
(Measured by core samples)
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Cap Thickness by Survey
Variability likely due to lateral position
inaccuracy
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Observations after Placement

• Chemical measurements showed good cap/sediment
  separation
• Seepage diverted by low permeability cap
  (Aquablok)
• Significant gas release during and subsequent to
  placement no evidence of contaminant release
• Gas accumulation with low permeability cap

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Chemical Data May 04 Sampling

• Data undergoing review
• No samples showed any detectable migration into
  active or sand cap layers beyond intermixing
  layer
• Occasional cores showed thin layer of fine
  grained sediment at surface of cap unconnected to
  underlying sediment
• Possible resuspension during capping (but no
  corresponding water column detection during
  capping)
• Possible new sediment deposition
• One sample showed 3 ppm total PAHs on surface of
  sand (coke breeze cap- near storm drain with
  occasional active oil seeps)

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Seepage rates in Anacostia
Nearshore
East
Offshore
West
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Seepage Rates Post Placement
Uncapped
Sand
Aquablok
Smith, 2004
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Sediment Camera Image Anacostia River
Bubble
Gas Voids
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Effects of Gas on Impermeable Cap Inclinometer
Placement
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FIGURE 2
Cap Deformation During the Period 4/16/4004
through 5/25/04 1500 hrs

Anacostia River Sediment Capping Research
Project Washington, D.C.
HydroQual, Inc.
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Selected Active Caps Total Material Costs

• AquaBlok (4-6)
• 3.00/ft2
• 27/yd2
• Coke (mat)
• 1.11-1.14/ft2 (1/ft2 mat)
• 10/yd2
• Apatite (6)
• 3.10 /ft2
• 28/yd2
• Sand (6 layer) (added to each of the above)
• 0.45/ ft2
• 4/yd2

All costs exclude shipping
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Cap Placement Rates

• Coke Breeze mat
• 0.4-0.9 yd2/hr
• Aquablok (3 inch dry target)
• 2.4 6.3 yd2/hr
• Sand/Apatite
• 1.4 33 yd2/hr
• All rates limited by startup issues on small
  areas
• Placement over large areas expected to be
  significantly greater

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Cap Placement Costs

• Demonstration construction costs not
  representative due to small size
• Although construction completed 2 weeks ahead of
  schedule and 20 under budget
• Large scale site (1000 acre)
• 25/yd2 materials
• Mobilization/demobilization 1 /yd2
• Cap placement 10/yd2
• Project Management 2/yd2
• Monitoring 10/yd2
• Miscellaneous 2/yd2
• Site Preparation
• Construction Management
• Design and Permits
• Sand capping cost Navigational dredging

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Lessons being Learned

• Innovative cap materials possible to place using
  conventional equipment with experienced
  contractor
• Possible to apply thin (6) layer of cap material
  using clamshell techniques
• Thickness criteria should be probabilistic
• Occasional deviations, typically near edges
• Intermixing in soft sediments small and
  manageable after near surface discharge of
  granular cap material.
• A laminated mat provides opportunities for
  controlled placement of light and/or high value
  materials (e.g. ? scale zero valent iron or
  activated carbon)
• Gas will find a path of release
• Plan for it and monitor for potential
  consequences
• Seemingly few consequences, at least in the
  absence of NAPL