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Title: Effect of air sparging on fate and transport of trichloroethylene in chambers with alfalfa plants

Abstract

To study the effect of air sparging in soil with trichloroethylene present as a dense nonaqueous phase, air was supplied through pipes installed at the bottom of two chambers planted with alfalfa. Air input rate was 2.14 L/m{sup 2}/day. The fate of trichloroethylene (TCE) was investigated by monitoring TCE concentration in both outflow groundwater and soil gas. Comparison of these results with those of the previous study without air sparging indicates that air sparging appreciably increases the groundwater concentration of TCE. The soil gas at the surface shows even greater concentration difference. The flux of TCE to the atmosphere is increased significantly by air input. Accordingly, the authors can conclude that air sparging improved mass transfer of TCE from the nonaqueous phase to groundwater phase. Air sparging appeared to negatively impact the health of the alfalfa because of the elevated TCE present in the vadose zone of the chamber.

Authors:
; ; ;  [1]
  1. Kansas State Univ., Manhattan, KS (United States)
Publication Date:
Sponsoring Org.:
Environmental Protection Agency, Washington, DC (United States)
OSTI Identifier:
585804
Report Number(s):
CONF-9705104-
Journal ID: ISSN 1054-8564; TRN: IM9810%%39
Resource Type:
Conference
Resource Relation:
Conference: 12. Annual conference on hazardous waste remediation, Kansas City, MO (United States), 20-22 May 1997; Other Information: PBD: 1997; Related Information: Is Part Of Proceedings of the 12. annual conference on hazardous waste research. Building partnerships for innovative technologies; Erickson, L.E.; Rankin, M.M.; Grant, S.C.; McDonald, J.P. [eds.]; PB: 586 p.
Country of Publication:
United States
Language:
English
Subject:
54 ENVIRONMENTAL SCIENCES; CHLORINATED ALIPHATIC HYDROCARBONS; SOILS; ALFALFA; ENVIRONMENTAL TRANSPORT; EXPOSURE CHAMBERS; GROUND WATER

Citation Formats

Zhang, Q., Hu, J., Erickson, L.E., and Davis, L.C. Effect of air sparging on fate and transport of trichloroethylene in chambers with alfalfa plants. United States: N. p., 1997. Web.
Zhang, Q., Hu, J., Erickson, L.E., & Davis, L.C. Effect of air sparging on fate and transport of trichloroethylene in chambers with alfalfa plants. United States.
Zhang, Q., Hu, J., Erickson, L.E., and Davis, L.C. 1997. "Effect of air sparging on fate and transport of trichloroethylene in chambers with alfalfa plants". United States. doi:.
@article{osti_585804,
title = {Effect of air sparging on fate and transport of trichloroethylene in chambers with alfalfa plants},
author = {Zhang, Q. and Hu, J. and Erickson, L.E. and Davis, L.C.},
abstractNote = {To study the effect of air sparging in soil with trichloroethylene present as a dense nonaqueous phase, air was supplied through pipes installed at the bottom of two chambers planted with alfalfa. Air input rate was 2.14 L/m{sup 2}/day. The fate of trichloroethylene (TCE) was investigated by monitoring TCE concentration in both outflow groundwater and soil gas. Comparison of these results with those of the previous study without air sparging indicates that air sparging appreciably increases the groundwater concentration of TCE. The soil gas at the surface shows even greater concentration difference. The flux of TCE to the atmosphere is increased significantly by air input. Accordingly, the authors can conclude that air sparging improved mass transfer of TCE from the nonaqueous phase to groundwater phase. Air sparging appeared to negatively impact the health of the alfalfa because of the elevated TCE present in the vadose zone of the chamber.},
doi = {},
journal = {},
number = ,
volume = ,
place = {United States},
year = 1997,
month =
}

Conference:
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  • Experiments were performed in a laboratory chamber to investigate the influence of alfalfa plants on the fate and transport of trichloroethylene (TCE) fed at 200 {micro}l/l concentration in the entering ground water. Concentrations of TCE in the aqueous and gas phases were regularly monitored in the chamber. Evapotranspirational fluxes of TCE were also reported from the soil to the headspace of the chamber. Numerical modeling of the fate of TCE in the vertical direction of this chamber was carried out using the Galerkin finite element approach. In this model, the partitioning of TCE between solid, aqueous, and gas phases wasmore » represented as rate-independent physical equilibrium processes. The boundary condition at the surface was modified to account for free volatilization of TCE to the headspace of the chamber across a thin atmospheric boundary layer. The simulation results were compared with experimental data on the transport of TCE. Results indicated that the water and air content distribution in the soil significantly impact the transport of TCE in subsurface soils.« less
  • Experimental investigations were carried out in the laboratory to study the impact of vegetation in bioremediating soil and groundwater contaminated with hazardous organic substances. A 90 cm long chamber with 2 U-shaped channels, each 10 cm in width and 35 cm in depth, was set up. Alfalfa plants were chosen and they have been growing in the channels under laboratory conditions for nearly 2 years. The channels were packed with fine sandy soil collected from near a landfill. The groundwater fed to one channel was water contaminated with toluene solution at saturated concentrations {at} 25 C, whereas, the other channelmore » was fed with water contaminated with phenol solution {at} 500 ppm (v/v). The contaminant concentrations in the groundwater of the channels were monitored at the sampling wells located along each of the channels. The influent and effluent flow rates from each channel were measured every day and recorded. Evapotranspiration significantly influenced the fate of the pollutants. Dispersion and adsorption processes in the channel were studied by introducing bromide tracer, as a broad pulse, into the toluene fed channel and by observing toluene and phenol concentrations, following a feed step change to pure water. Tracer studies indicated that short-circuiting in the end of the channel was quite significant. Models which were previously developed to describe the fate of the contaminants in variably-saturated soils in the presence of vegetation are being employed to simulate the fate of these hazardous organic substances in the laboratory chamber.« less
  • The fate of several volatile organic compounds including phenol, toluene, 1,1,1-trichloroethane, trichloroethylene, and chloroform have been investigated in sandy soil with alfalfa plants growing in the soil. A mathematical model has been developed to follow the fate of water, contaminant, root exudates produced by the plants, oxygen, and microbial growth. Concentrations of the contaminants have been measured in the gas phase, plant biomass, and ground water. Headspace analysis of the gas in the enclosed chamber showed that small quantities of the chlorinated compounds migrated into the gas phase above the alfalfa plants. Research is in progress to investigate the transportmore » of volatile contaminants through plants. The concentrations of the volatile contaminants which evolved with the transpired water are diluted significantly as they enter the gas phase because of the small amount of water that is soluble in air at ambient temperatures. Vegetated bioremediation systems have been employed at several field sites in the U.S. and in several other countries. The model can be used to design fields of vegetation which function as solar driven pump-and-treat processes; these systems are very inexpensive. 17 refs.« less
  • Due to its carcinogenic potential, the kinetics of TCE metabolism to its primary oxidative products was studied in B6C3F1 mice exposed to TCE vapor concentrations of 100, 300 and 600 ppm in inhalation chambers. TCE and its metabolites were quantified in the blood, liver, kidney, fat and lungs by GC analysis. A physiologically-based pharmacokinetic (PB-PK) model was used to simulate the distribution and metabolism of TCE in the body using SIMUSOLV. The PB-PK model structure consisted of liver, kidney, lung, richly and slowly perfused tissues, and fat that were interconnected by arterial and venous blood pools. Tissue:blood partition coefficients formore » fat, liver, lung and slowly and rapidly perfused tissues and a blood:air partition coefficient were measured in the laboratory for TCE and its metabolites. The in vivo Michaelis-Menten metabolic constants, Vmaxc and Km, were determined for TCE in gas uptake studies. These values were Km = 0.2 mg/L and Vmaxc = 31.4 mg/hr-kg and they were used in the current PB-PK model to describe the metabolism of TCE to its primary oxidative metabolites. The results suggest that such models can be a useful tool in the evaluation of the impacts of environmental contaminants in any species for which adequate physiological data are available.« less
  • Originally described for legumes by Lorenz Hiltner in 1904, the rhizosphere is a zone of increased microbial density and activity at the root-soil interface. Plant roots secrete a variety of organic compounds into the surrounding soil which lubricate the root as well as provide nourishment for and attract microorganisms. The exudates, along with root cortical cells sloughed off through abrasive actions with the soil, provide a rich nutrient source for growth of the microbial community in the rhizosphere. Studies examining the fate of pesticides applied to rhizosphere soil or microorganisms isolated from the root zone have revealed a marked decreasemore » in persistence of these compounds. These early findings in pesticide research, along with the promise of a cost-effective remediation strategy, provided the incentive to explore whether vegetation could be used to promote microbial degradation of hazardous organic compounds. In experiments which are presented, the fate of {sup 14}C-TCE in whole plant systems composed of soil and vegetation from a contaminated field site was monitored. Findings from these experiments provide further evidence that vegetation may play an important role in remediation of TCE- contaminated soils. In addition, the data reveal the magnitude of plant uptake of hazardous organic compounds treated in this manner, and thus potentially gain entry to human and/or wildlife food chains. 11 refs., 2 figs., 1 tab.« less