Modeling 3D-CSIA data

Modeling 3D-CSIA data: Carbon, chlorine, and hydrogen isotope fractionation during reductive dechlorination of TCE to ethene

van Breukelen, B.M. (TU Delft Sanitary Engineering)
Thouement, H.A.A. (TU Delft Sanitary Engineering)
Stack, Philip E. (Scotland's Rural College)
Vanderford, Mindy (HydroGeoLogic)
Philp, Paul (University of Oklahoma)
Kuder, Tomasz (University of Oklahoma)

2017

Reactive transport modeling of multi-element, compound-specific isotope analysis (CSIA) data has great potential to quantify sequential microbial reductive dechlorination (SRD) and alternative pathways such as oxidation, in support of remediation of chlorinated solvents in groundwater. As a key step towards this goal, a model was developed that simulates simultaneous carbon, chlorine, and hydrogen isotope fractionation during SRD of trichloroethene, via cis-1,2-dichloroethene (and trans-DCE as minor pathway), and vinyl chloride to ethene, following Monod kinetics. A simple correction term for individual isotope/isotopologue rates avoided multi-element isotopologue modeling. The model was successfully validated with data from a mixed culture Dehalococcoides microcosm. Simulation of Cl-CSIA required incorporation of secondary kinetic isotope effects (SKIEs). Assuming a limited degree of intramolecular heterogeneity of δ³⁷Cl in TCE decreased the magnitudes of SKIEs required at the non-reacting Cl positions, without compromising the goodness of model fit, whereas a good fit of a model involving intramolecular CCl bond competition required an unlikely degree of intramolecular heterogeneity. Simulation of H-CSIA required SKIEs in H atoms originally present in the reacting compounds, especially for TCE, together with imprints of strongly depleted δ²H during protonation in the products. Scenario modeling illustrates the potential of H-CSIA for source apportionment.

Chlorinated ethenes
Contaminated sites
Natural attenuation
Reactive transport modeling
Reductive dechlorination
Stable isotopes

http://resolver.tudelft.nl/uuid:f1ba127b-c41e-43fb-a6e2-d2786ed63ffd

https://doi.org/10.1016/j.jconhyd.2017.07.003

0169-7722

Journal of Contaminant Hydrology, 204, 79-89

Institutional Repository

journal article

© 2017 B.M. van Breukelen, H.A.A. Thouement, Philip E. Stack, Mindy Vanderford, Paul Philp, Tomasz Kuder