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Louis J Thibodeaux

Publications and source records attributed to Louis J Thibodeaux.

4 recordsLinked to original sources
PubMed2005

Field observation and modeling of dissolved fraction sediment-water exchange coefficients for PCBs in the Hudson River.

Chemical fate and transport models that simulate sediment-water exchange of contaminants typically employ empirically determined sediment-water exchange coefficients for the dissolved fraction to describe the net effect of poorly understood mechanisms. This paper presents field-derived observations of the coefficient for 12 PCB congeners and two PCB mixtures in the Thompson Island Pool, Hudson River, and also presents an evaluation of a theoretical sediment-water exchange model. An extensive PCB data set was used to compute apparent coefficients for PCBs in the pool. Average exchange coefficients for the 12 congeners ranged from 2.6 to 18.8 cm/ day, and results showed a strong seasonal dependence. Peak coefficient values occurred in mid-May to early July, preceding peak water temperatures by 1 month and lagging the spring high-flow period. The coefficients increase with increasing partition coefficients, suggesting a dependence on congener properties. The large magnitude of the coefficients and the variation among the congeners is inconsistent with the pore-water molecular-diffusion transport process. A theory-based, mechanistic two-layer model reproduces the nonlinear relationship between the sediment-water exchange coefficients and partition coefficients. This model includes transfer through the mixed sediment layer by bioturbation and diffusion transfer through a water-side boundary layer governed by flow velocity. Results suggest that this algorithm can provide increased accuracyto future system-level fate and transport models for hydrophobic chemicals. The seasonal variation in the transfer coefficient appears to be a poorly understood interaction of physical and biological processes and merits further study.

Diffusion↗
PubMed2004

Obtaining quantitative vapor emissions estimates of polychlorinated biphenyls and other semivolatile organic compounds from contaminated sites.

Soils contaminated with polychlorinated biphenyls (PCBs) and other semivolatile organic compounds (SVOCs) represent a potentially major, ongoing source of these compounds to the environment, especially during warmer temperatures. A great deal of work has been devoted to understanding the mechanisms that govern the vaporization of SVOCs from soil, but to date, few quantitative estimates have been published regarding emissions from contaminated sites. The present paper describes methods for obtaining quantitative estimates of SVOCs from soils based on flux chamber measurements, modeling, and ambient air measurements. On wet (i.e., H2O) soils, SVOCs at very low chemical loading levels on the adsorption sites (the so-called critical chemical concentration, critical loading, or saturation concentration) will behave, for volatilization purposes, as the pure-liquid substance would. For one soil, the PCB critical concentration was determined to be 775 ppm (95% confidence interval, 5.40E+02). Flux chamber-measured emissions from two contaminated sites were used and compared to model estimated values. The results agree reasonably well and indicate that the modeling approach used provided a conservative upper bound on the emissions. These approaches can be used to develop emissions estimates for SVOC-contaminated sites and inputs to air dispersion models.

Air↗
PubMed2002

Volatilization of contaminants from suspended sediment in a water column during dredging.

Remedial dredging of contaminated bed sediments in rivers and lakes results in the suspension of sediment solids in the water column, which can potentially be a source for evaporation of hydrophobic organic compounds (HOCs) associated with the sediment solids. Laboratory experiments were conducted in an oscillating grid chamber to simulate the suspension of contaminated sediments and flux to air from the surface of the water column. A contaminated field sediment from Indiana Harbor Canal (IHC) and a laboratory-inoculated University Lake (UL) sediment, Baton Rouge, LA, were used in the experiments, where water and solids concentration and particle size distribution were measured in addition to contaminant fluxes to air. A transient model that takes into account contaminant desorption from sediment to water and evaporation from the water column was used to simulate water and sediment concentrations and air fluxes from the solids suspension. In experiments with both sediments, the total suspended solids (TSS) concentration and the average particle diameter of the suspended solids decreased with time. As expected, the evaporative losses were higher for compounds with higher vapor pressure and lower hydrophobicity. For the laboratory-inoculated sediment (UL), the water concentrations and air fluxes were high initially and decreased steadily implying that contaminant release to the water column from the suspended solids was rapid, followed by evaporative decay. For the field sediments (IHC), the fluxes and water concentrations increased initially and subsequently decreased steadily. This implied that the initial desorption to water was slow and that perhaps the presence of oil and grease and aging influenced the contaminant release. Comparison of the model and experimental data suggested that a realistic determination of the TSS concentration that can be input into the model was the most critical parameter for predicting air emission rates.

Engineering↗