Binning, Philip John

Bjerg, Poul Løgstrup

Broholm, Mette Martina

Chambon, Julie Claire Claudia

Damgaard, Ida

Hunkeler, Daniel

Online Research Database In Technology

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Downloaded from orbit.dtu.dk on: Dec 18, 2017Combining numerical modeling and isotope data to assess reductive dechlorinationand diffusion in clay tillsChambon, Julie Claire Claudia; Damgaard, Ida; Broholm, Mette Martina; Hunkeler, Daniel; Binning, PhilipJohn; Bjerg, Poul LøgstrupPublished in:Geophysical Research AbstractsPublication date:2011Document VersionPublisher's PDF, also known as Version of recordLink back to DTU OrbitCitation (APA):Chambon, J. C. C., Damgaard, I., Broholm, M. M., Hunkeler, D., Binning, P. J., & Bjerg, P. L. (2011). Combiningnumerical modeling and isotope data to assess reductive dechlorination and diffusion in clay tills. GeophysicalResearch Abstracts, 13, EGU2011-7834.Geophysical Research AbstractsVol. 13, EGU2011-7834, 2011EGU General Assembly 2011© Author(s) 2011Combining numerical modeling and isotope data to assess reductivedechlorination and diffusion in clay tillsJulie Chambon (1), Ida Damgaard (1), Mette M. Broholm (1), Daniel Hunkeler (2), Philip J. Binning (1), andPoul L. Bjerg (1)(1) Technical University of Denmark, DTU Environment, Kgs. Lyngby, Denmark (jccc@env.dtu.dk / +4545932850), (2)University of Neuchatel, SwitzerlandEnhanced Reductive Dechlorination (ERD) has been successfully used in high permeability media, such as sandaquifers, and is considered to be a promising technology for low permeability settings. One of the main challengesin low-permeability settings is to obtain good contact between the injected bacteria and electron donor and thecontaminants trapped in the matrix. The objective of this study is to assess whether the degradation processestake place only in higher permeability zones in the clay till such as sand lenses or stringers, or if degradationprocesses also develop within the clay till matrix. Isotope fractionation data, biogeochemical data and numericalmodelling is used to identify the zones in the clay till where natural dechlorination has occurred. The results canbe further combined with other data (molecular biological tools, pore size constrains, etc. . . ) in order to identifythe controlling parameters that allow degradation in the matrix.Reactive transport models coupled with isotope fractionation are widely used to document natural attenua-tion along flowpathes in high permeability porous media. Isotope fractionation due to diffusion is often negligiblein advection dominating systems, but diffusion is the dominant transport process in the clay matrix, and theheavier isotopes are expected to diffuse slower than the lighter ones. But it can be difficult to distinguish whetherisotope fractionation is caused by diffusion or degradation. In the present work, modelling was used to investigateseveral conceptual models regarding dechlorination locations (in high permeability zones, in the whole matrix, inlimited bioactive zones within the matrix). The model includes diffusion in the matrix, sequential dechlorination,isotope fractionation due to degradation and isotope fractionation due to diffusion in the clay matrix.At Vadsby, Hedehusene, Denmark, chlorinated solvents were spilled during the 1960-70’s, resulting in con-tamination of the clay till and the underlying sandy layer (15 meters below surface). The clay till is heavilycontaminated between 4 and 15 mbs, both with the mother compounds PCE/TCE and TCA and the daughterproducts (DCE, VC, ethene, DCA), indicating the occurrence of natural dechlorination of both PCE/TCE andTCA. Intact core samples of length 0.5m have been collected from the source zone (between 6 and 12 mbs).Concentrations and stable isotope fractionation of the mother compounds and their daughter products, as well asredox parameters, fatty acids and microbial data, were analyzed with discrete sub-sampling along the cores. Moresamples (each 5 mm) were collected around the observed higher permeability zones such as sand lenses, sandstringers and fractures, where a higher degradation activity was expected.In several cores, the concentration profiles of TCE and daughter products indicate that degradation is likelyto have occurred in and around the high permeability features, as well as further within the clay matrix. Theisotope data must be combined with numerical modelling to distinguish between transport processes (diffu-sion/sorption) and degradation, and support the identification of bioactive zones within the clay till. Improvedunderstanding of reductive dechlorination in clay tills is useful for improving the reliability of risk assessment andthe design of enhanced reductive dechlorination remediation schemes for chlorinated solvents.

Combining numerical modeling and isotope data to assess reductive dechlorination and diffusion in clay tills

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Combining numerical modeling and isotope data to assess reductive dechlorination and diffusion in clay tills

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