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Cinétiques de dégradation des solvants chlorés dans les eaux souterraines - Approches multi-échelles du laboratoire au site réel

Abstract : Since the 50's, the contamination of soils and groundwater by chlorinated solvents significantly increases. These volatile organic compounds are also widely used in industry and the majority of them are considered potential carcinogenic chemicals for human beings. This work is particularly focalised on an innovative strategy of polluted sites management : Natural Attenuation. Several mechanisms govern this approach and among them, it is direct anaerobic reductive dechlorination which seems to be the most significative degradation process. The aim of the work was to evaluate whether the study of reductive dechlorination at various different observation scales allowed for a better characterization of Natural Attenuation on a real site. The site is a still active industrial complex where a PCE (tetrachloroethylene) source zone was discovered. Moreover, another regions contaminated by mineral oils were also characterized. Physicochemical groundwater monitoring enabled to demonstrate the occurence of PCE degradation byproducts directly above the source zone, such as cis-1,2-dichloroethylene and Vinyl Chloride (VC). According to the solution of Domenico et al. (1987), the approximate transport modeling proved that the plume of dissolved organochlorinated compounds fluctuated laterally. In order to confirm the occurrence of direct reductive dechlorination at different locations of the site, several batch reactors were prepared from subsoils and groundwater. Results indicated that complete biodegradation of PCE to ethene is very localized at the site ; furthermore, the growth of dechlorinating bacteria seems to be highly restricted to the content of dissolved organic matter. The experiments carried out in a lab column provided interesting informations about the influence of sulphate and organic matter level on PCE biodegradation. The fittings of first order degradation rates with Phreeqc-2.0 demonstrated that sulfate-reduction and complete transformation of PCE to cis-1,2-DCE could be simulated in specific physicochemical conditions. According to a specific monitoring campaign, different runs carried out with the hydrodynamic model of transport and biodegradation showed that the plume of organochlorinated pollution is narrow because of fast groundwater flux. Therefore, the plume migrates quickly. Biodegradation modeling was a difficult operation, due to difficulties in fitting of chloroethenes concentrations, which are spatially and temporally heterogeneous. At the field scale, estimated degradation rates seem to be reduced, compared to the data measured at laboratory scale.
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Arnaud Mangeret. Cinétiques de dégradation des solvants chlorés dans les eaux souterraines - Approches multi-échelles du laboratoire au site réel. Géochimie. Université Michel de Montaigne - Bordeaux III, 2009. Français. ⟨tel-00650447⟩

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