Volatile Release from Dredged Materials

1
Volatile Release from Dredged Materials

• K. T. Valsaraj, L J Thibodeaux, D D Reible, R
  Ravikrishna
• Gordon A. and Mary Cain Department of Chemical
  Engineering
• Louisiana State University
• Baton Rouge, LA 70803
• Presentation for the Symposium on
• 25 Years of Hazardous Substance Research at LSU
• May 2, 2003

2

• Background
• Dredging (Navigational and Remedial)
• Storage of Dredged Sediment in Confined Disposal
  Facilities (CDFs)
• Dredged Material contaminated with Hydrophobic
  Organic Compounds (HOCs) (eg Polynuclear
  Aromatic Hydrocarbons or PAHs)
• Certain PAHs are suspected carcinogens
• Human Exposure Risk due to volatilization of HOCs
  from exposed dredged materials in CDFs

3

• Motivation
• Volatilization is a significant mechanism for
  contaminant release from CDFs US ACE/WES.
• Air concentrations (of PCBs) near CDFs and other
  exposed sediment surfaces noted.
• Robust models required to predict volatilization
  rates of HOCs from exposed sediments in a CDF,
  which can be used to assess human exposure risk.
• Scarce laboratory or field data are available to
  validate existing models.

4
Confined Disposal Facilities (CDFs)
5
Pathways of loss from CDF
During Filling
After Filling
6

• Objectives
• Obtain emission flux data of selected tracer PAHs
  in laboratory experiments
• Study the effects of various factors on emission
  fluxes
• air relative humidity, moisture and oil and
  grease in sediment, reworking of sediment,
  sediment capping, cracks in sediment and sediment
  resuspension
• Validate mathematical models with the laboratory
  data
• Obtain flux data from a pilot scale CDF and
  compare with model predicted fluxes
• Use pilot scale data with an atmospheric
  dispersion model to evaluate human exposure risk

7
Contaminant Volatilization - A Conceptual Model
8
Effect of Sediment Moisture Content
9
Effect of Air Relative Humidity
10
Effect of Sediment Reworking
11
Effect of OG on emission
12
Comparison of Flux from Capped and Uncapped
sediments
13
Pilot Scale CDF

• Test conducted at Waterways Experiment Station,
  Vicksburg, MS
• Dredged material from Indiana Harbor Canal (IHC)
• Periodic flux measurements with modified flux
  chamber
• Meteorological station to monitor wind speed and
  direction, relative humidity and temperature,
  soil temperature and soil moisture
• Core sample sectioning for concentration and oil
  profile
• Rainfall simulation over the model CDF
• Reworking of dredged material surface
• Comparison of PHE flux with model
• Application of experimental flux in an
  atmospheric dispersion model to assess human
  exposure risk

14
Pilot Scale CDF- Experimental Setup
15
Weather and Sediment Parameters - Pilot Scale CDF
16
Experimental and Model Flux - Phenanthrene
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Resuspension of Sediment During Dredging and in
a CDF

• Significant air concentrations observed at
  certain dredging hot spots
• No direct measurements of air emissions resulting
  from sediment resuspension available
• Oscillating grids extensively used to recreate
  desired turbulence in water columns
• Modified oscillating grid flux chambers designed
  to generate desired suspended sediment
  concentrations
• Flux measurements to air and corresponding
  aqueous phase concentrations

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Resuspension and Volatilization
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Experimental Set up - Flux measurement
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Total Suspended Sediment (TSS)
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Flux to air at different TSS
22
Mass transfer coefficient versus TKE
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Conclusions

• Is evaporation of HOCs from a CDF important?
• Long term emissions from exposed sediment not
  significant after the CDF is completely filled
• Emissions are relatively higher in the initial
  stages and during reworking
• Model - a reliable tool to assess, monitor and
  manage exposure risk due to volatilization?
• Satisfactory prediction of emission rates by the
  model
• Useful for siting and emission monitoring
  decisions
• Models to be included in the ADDAMs suite of the
  US Army Corps of Engineers risk assessment
  procedure

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Conclusions

• Laboratory Studies
• Flux is high following exposure and decreases
  rapidly to attain a slowly falling pseudo steady
  state flux
• Emissions at the surface is air-side resistance
  controlled initially, progressively becoming
  sediment side resistance controlled as surface
  depletion occurs
• Emission from a dry surfaces are lower than that
  from damp or wet surfaces due to differences in
  adsorption on the sediment surface
• Oil and grease in sediment act as an additional
  compartment resulting in increased partitioning
  and resultant lower equilibrium concentrations of
  the contaminant in the pore spaces
• Capping of sediment results in significant
  reduction of surface emissions
• Satisfactory agreement between model and
  experimental data

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Conclusions

• Pilot Scale Study
• Contaminant flux was high initially and decreased
  rapidly
• Significant compaction of sediment due to water
  evaporation resulted in changes in transport
  properties
• Reworking of dredged material resulted in
  increase of flux
• Models used with laboratory data agreed
  satisfactorily with the pilot scale phenanthrene
  flux data
• Atmospheric dispersion models used with pilot
  scale flux data showed ambient air concentrations
  lower than OSHA regulations for phenanthrene

26
Conclusions

• Resuspension of sediment and dredged materials
• Air Emissions of tracers HOCs were measured from
  a sediment suspension generated using an
  oscillating grid
• Corresponding suspended solids concentrations and
  aqueous concentrations of the HOCs measured
• Flux to air and water concentrations were
  directly proportional to the suspended sediment
  concentrations

27
Acknowledgements

• U. S. EPA (HSRC SSW)
• U.S. Army Corps of Engineers
• Graduate Student R Ravikrishna
• Undergraduates Greg, Louis, Toriano, Sonal
• Univ. of Minnesota J Gulliver, J J Orlins
• US ACE C B Price, J M Brannon, S Yost, T Myers