title: Quantification of Degradation of Chlorinated Hydrocarbons in Saturated Low Permeability Sediments Using Compound-Specific Isotope Analysis.
abstract: This field and modeling study aims to reveal if degradation of chlorinated hydrocarbons in low permeability sediments can be quantified using compound-specific isotope analysis (CSIA). For that purpose, the well-characterized Borden research site was selected, where an aquifer-aquitard system was artificially contaminated by a three component chlorinated solvent mixture (tetrachloroethene (PCE) 45 vol %, trichloroethene (TCE) 45 vol %, and chloroform (TCM) 10 vol %). Nearly 15 years after the contaminant release, several high-resolution concentration and CSIA profiles were determined for the chlorinated hydrocarbons that had diffused into the clayey aquitard. The CSIA profiles showed large shifts of carbon isotope ratios with depth (up to 24‰) suggesting that degradation occurs in the aquitard despite the small pore sizes. Simulated scenarios without or with uniform degradation failed to reproduce the isotope data, while a scenario with decreasing degradation with depth fit the data well. This suggests that nutrients had diffused into the aquitard favoring stronger degradation close to the aquifer-aquitard interface than with increasing depth. Moreover, the different simulation scenarios showed that CSIA profiles are more sensitive to different degradation conditions compared to concentration profiles highlighting the power of CSIA to constrain degradation activities in aquitards.
authors.affiliation: Centre for Hydrogeology & Geothermics (CHYN), University of Neuchâtel , Rue Emil Argand 11, CH-2000 Neuchâtel, Switzerland.
authors.forename: Philipp
authors.initials: P
authors.lastname: Wanner
authors.affiliation: G360 Centre for Applied Groundwater Research, School of Engineering, University of Guelph , 50 Stone Road East, Guelph, Ontario, Canada N1G 2W1.
authors.forename: Beth L
authors.initials: BL
authors.lastname: Parker
authors.affiliation: G360 Centre for Applied Groundwater Research, School of Engineering, University of Guelph , 50 Stone Road East, Guelph, Ontario, Canada N1G 2W1.
authors.forename: Steven W
authors.initials: SW
authors.lastname: Chapman
authors.affiliation: Department of Earth and Environmental Sciences, University of Waterloo , 200 University Avenue West, Waterloo, Ontario, Canada N2L 3GI.
authors.forename: Ramon
authors.initials: R
authors.lastname: Aravena
authors.affiliation: Centre for Hydrogeology & Geothermics (CHYN), University of Neuchâtel , Rue Emil Argand 11, CH-2000 Neuchâtel, Switzerland.
authors.forename: Daniel
authors.initials: D
authors.lastname: Hunkeler
mesh_terms: D001673:Biodegradation, Environmental; D002247:Carbon Isotopes; D006843:Hydrocarbons, Chlorinated; D010539:Permeability; D013750:Tetrachloroethylene; D014241:Trichloroethylene; D014874:Water Pollutants, Chemical
chemical_list: D002247:Carbon Isotopes; D006843:Hydrocarbons, Chlorinated; D014874:Water Pollutants, Chemical; D014241:Trichloroethylene; D013750:Tetrachloroethylene