Quantification of Degradation of Chlorinated Hydrocarbons in Saturated Low Permeability Sediments Using Compound-Specific Isotope Analysis
Author(s)
Parker, Beth L.
Chapman, Steven W.
Aravena, Ramon
Date issued
May 2016
In
Environmental Science & Technology
No
50
From page
5622
To page
5630
Reviewed by peer
1
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 highresolution 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.
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 highresolution 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.
Publication type
journal article
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