title: Improved constraints on in situ rates and on quantification of complete chloroethene degradation from stable carbon isotope mass balances in groundwater plumes.
abstract: Spills of chloroethenes (CEs) at industrial and urban sites can create groundwater plumes in which tetrachloro- and trichloroethene sequentially degrade to dichloroethenes, vinyl chloride (VC) and ethene, or ethane under reducing conditions. For detoxification, degradation must go beyond VC. Assessments based on ethene and ethane, however, are difficult because these products are volatile, may stem from alternative sources, can be further transformed and are not always monitored. To alternatively quantify degradation beyond VC, stable carbon isotope mass balances have been proposed where concentration-weighted CE isotope ratios are summed up and compared to the original source isotope ratio. Reported assessments, however, have provided not satisfactorily quantified results entailing greatly differing upper and lower estimates. This work proposes an integrative approach to better constrain the extent of total chloroethene degradation in groundwater samples. It is based on fitting of measured concentration and compound-specific stable carbon isotope data to an analytical reactive transport equation simulating steady-state plumes in two dimensions using an EXCEL spreadsheet. The fitting also yields estimates of degradation rates, of source width and of dispersivities. The approach is validated using two synthetic benchmark cases where the true extent of degradation is well known, and using data from two real field cases from literature.
authors.affiliation: Aix-Marseille Université-CNRS, Laboratoire Chimie Environnement FRE 3416, Marseille, France. Electronic address: patrick.hohener@univ-amu.fr.
authors.forename: Patrick
authors.initials: P
authors.lastname: Höhener
authors.affiliation: Helmholtz Zentrum München, Institute of Groundwater Ecology, Ingolstädter Landstr. 1, 85764 Neuherberg, Germany.
authors.forename: Martin
authors.initials: M
authors.lastname: Elsner
authors.affiliation: Isodetect GmbH Ingolstädter Landstr. 1, 85764 Neuherberg, Germany.
authors.forename: Heinrich
authors.initials: H
authors.lastname: Eisenmann
authors.affiliation: ENSEGID, EA 4592, 1 allée Daguin, 33607 Pessac, France.
authors.forename: Olivier
authors.initials: O
authors.lastname: Atteia
mesh_terms: D001673:Biodegradation, Environmental; D002247:Carbon Isotopes / Q000032:analysis; D060587:Groundwater / Q000032:analysis* / Q000737:chemistry; D014241:Trichloroethylene / Q000378:metabolism*; D014752:Vinyl Chloride / Q000032:analysis* / Q000378:metabolism; D014874:Water Pollutants, Chemical / Q000032:analysis / Q000378:metabolism*
chemical_list: D002247:Carbon Isotopes; D014874:Water Pollutants, Chemical; D014241:Trichloroethylene; D014752:Vinyl Chloride
keywords: Bioremediation; Fitting; Modeling; Natural attenuation; Reactive transport