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Bouchard, Daniel

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Bouchard, Daniel
Affiliation principale
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https://libra.unine.ch/handle/123456789/30594

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  • Publication
    Accès libre
    Application of Diagnostic Tools to Evaluate Remediation Performance at Petroleum Hydrocarbon-Impacted Sites
    (2018-9)
    Bouchard, Daniel 
    ;
    Hunkeler, Daniel 
    ;
    Madsen, E.L.
    ;
    Buscheck, Thomas
    ;
    Daniels, E.
    ;
    Kolhatkar, R.
    ;
    De Rito, C. M.
    ;
    Aravena, Ramon
    ;
    Thomson, N.
    In situ treatment technologies for petroleum hydrocarbon-impacted sites (e.g., multiphase extraction, air sparging, soil vapor extraction, or in situ chemical oxidation) usually rely on a specific chemical, microbial, or physical contaminant removal process. However, target contaminant concentrations can also vary due to other co-occurring processes (e.g. delivery of remedial fluids, natural variability), which can confound the ability to demonstrate treatment efficiency. This technical note proposes a methodology that integrates several diagnostic tools to assess treatment performance. Stable isotope methods and biomarkers were selected because they provide process-specific and, often, also compound-specific information on contaminant removal. The isotope tools include compound-specific isotope analysis that can be used to discriminate between a broad range of removal processes, and isotope analysis of oxidants and degradation end products to assess overall transformation of hydrocarbons. The biomarkers cover characteristic metabolites and functional genes on a mRNA rather than DNA level to understand biological activity more carefully. This technical note integrates information from laboratory and field studies, especially controlled-field experiments where the tools have been evaluated side-by-side for different treatment methods. A tiered approach is proposed to deploy the tools in a stepwise manner until sufficient information is obtained to confidently identify the mass removal processes of interest and demonstrate efficacy of the intended treatment mechanism. The order of tool application considers the type of information that can be gained, the level of certainty, and the ease of implementation. The objective of this technical note is to enable widespread use of these diagnostic tools with the motivation to improve the efficacy of in situ treatment systems. © 2018, National Ground Water Association
  • Publication
    Accès libre
    Diagnostic Tools to Assess Mass Removal Processes During Pulsed Air Sparging of a Petroleum Hydrocarbon Source Zone
    (2018-6)
    Bouchard, Daniel 
    ;
    Marchesi, Massimo
    ;
    Madsen, Eugen L.
    ;
    DeRito, Christoph
    ;
    Thomson, Neil R.
    ;
    Aravena, Ramon
    ;
    Barker, Jim
    ;
    Buscheck, Thomas
    ;
    Kolhatkar, Ravi
    ;
    Daniels, Eric J.
    ;
    Hunkeler, Daniel 
    During remediation of contaminated aquifers, diagnostic tools can help evaluate whether an intended mass removal process was successfully initiated and acted on specific contaminants of concern. In this study, several diagnostic tools were tested in a controlled‐release in situ air sparging experiment that focused on the treatment of target hydrocarbons (e.g., benzene, toluene, ethylbenzene, and xylenes). The tools included compound‐specific isotope analysis (CSIA), expression of functional genes (mRNA), and metabolites characteristic of aerobic and anaerobic biodegradation. Total and compound‐specific mass balances were established and used, along with traditional monitoring parameters, to validate the results from the various tools. CSIA results indicated biodegradation as the main process contributing to benzene and toluene removal. Removal process‐specific isotope shifts were detected in groundwater as well as in the system effluent gas. CSIA, metabolite, and mRNA biomarkers consistently indicated that both aerobic and anaerobic biodegradation of benzene and toluene occurred, but that their relative importance evolved over time and were related to the treatment system operation. While the indicators do not allow quantification of the mass removed, they are particularly useful to identify if a removal process has been initiated, and to track relative changes in the predominance of in situ contaminant attenuation processes resulting from remediation efforts.
  • Publication
    Accès libre
    Carbon Isotope Fractionation during Diffusion and Biodegradation of Petroleum Hydrocarbons in the Unsaturated Zone: Field Experiment at Værløse Airbase, Denmark, and Modeling
    (2008)
    Bouchard, Daniel 
    ;
    Hunkeler, Daniel 
    ;
    Gaganis, Petros
    ;
    Aravena, Ramon
    ;
    Höhener, Patrick
    ;
    Broholm, Mette M.
    A field experiment was conducted in Denmark in order to evaluate the fate of 13 volatile organic compounds (VOCs) that were buried as an artificial fuel source in the unsaturated zone. Compound-specific isotope analysis showed distinct phases in the 13C/12C ratio evolution in VOC vapors within 3 m from the source over 114 days. At day 3 and to a lesser extent at day 6, the compounds were depleted in 13C by up to −5.7‰ with increasing distance from the source compared to the initial source values. This trend can be explained by faster outward diffusion of the molecules with 12C only compared to molecules with a 13C. Then, the isotope profile leveled out, and several compounds started to become enriched in 13C by up to 9.5‰ with increasing distance from the source, due to preferential removal of the molecules with 12C only, through biodegradation. Finally, as the amount of a compound diminished in the source, a 13C enrichment was also observed close to the source. The magnitude of isotope fractionation tended to be larger the smaller the mass of the molecule was. This study demonstrates that, in the unsaturated zone, carbon isotope ratios of hydrocarbons are affected by gas-phase diffusion in addition to biodegradation, which was confirmed using a numerical model. Gas-phase diffusion led to shifts in δ13C >1‰ during the initial days after the spill, and again during the final stages of source volatilization after >75% of a compound had been removed. In between, diffusion has less of an effect, and thus isotope data can be used as an indicator for hydrocarbon biodegradation.