Chlorinated ethene plume evolution after source thermal remediation: Determination of degradation rates and mechanisms
Author(s)
Alexandra Marie, Murray
Cecilie B., Ottosen
Julien, Maillard
Christof, Holliger
Anders, Johansen
Lærke, Brabæk
Inge Lise, Kristensen
Jeremy, Zimmermann
Broholm, Mette M.
Date issued
September 2019
In
Journal of Contaminant Hydrology
No
227
From page
103551
To page
103568
Reviewed by peer
1
Subjects
Stable isotopes Molecular biology Dehalogenimonas spp. Biodegradation Abiotic degradation Multiple lines of evidence
Abstract
The extent, mechanism(s), and rate of chlorinated ethene degradation in a large tetrachloroethene (PCE) plume
were investigated in an extensive sampling campaign. Multiple lines of evidence for this degradation were
explored, including compound-specific isotope analysis (CSIA), dual C-Cl isotope analysis, and quantitative realtime
polymerase chain reaction (qPCR) analysis targeting the genera Dehalococcoides and Dehalogenimonas and
the genes vcrA, bvcA, and cerA. A decade prior to this sampling campaign, the plume source was thermally
remediated by steam injection. This released dissolved organic carbon (DOC) that stimulated microbial activity
and created reduced conditions within the plume. Based on an inclusive analysis of minor and major sampling
campaigns since the initial site characterization, it was estimated that reduced conditions peaked 4 years after
the remediation event. At the time of this study, 11 years after the remediation event, the redox conditions in the
aquifer are returning to their original state. However, the DOC released from the remediated source zone
matches levels measured 3 years prior and plume conditions are still suitable for biotic reductive dechlorination.
Dehalococcoides spp., Dehalogenimonas spp., and vcrA, bvcA, and cerA reductive dehalogenase genes were detected
close to the source, and suggest that complete, biotic PCE degradation occurs here. Further downgradient,
qPCR analysis and enriched δ13C values for cis-dichloroethene (cDCE) suggest that cDCE is biodegraded in a
sulfate-reducing zone in the plume. In the most downgradient portion of the plume, lower levels of specific
degraders supported by dual C-Cl analysis indicate that the biodegradation occurs in combination with abiotic
degradation. Additionally, 16S rRNA gene amplicon sequencing shows that organizational taxonomic units
known to contain organohalide-respiring bacteria are relatively abundant throughout the plume. Hydraulic
conductivity testing was also conducted, and local degradation rates for PCE and cDCE were determined at
various locations throughout the plume. PCE degradation rates from sampling campaigns after the thermal
remediation event range from 0.11 to 0.35 yr−1. PCE and cDCE degradation rates from the second to the third
sampling campaigns ranged from 0.08 to 0.10 yr−1 and 0.01 to 0.07 yr−1, respectively. This is consistent with
cDCE as the dominant daughter product in the majority of the plume and cDCE degradation as the time-limiting
step. The extensive temporal and spatial analysis allowed for tracking the evolution of the plume and the lasting
impact of the source remediation and illustrates that the multiple lines of evidence approach is essential to
elucidate the primary degradation mechanisms in a plume of such size and complexity.
were investigated in an extensive sampling campaign. Multiple lines of evidence for this degradation were
explored, including compound-specific isotope analysis (CSIA), dual C-Cl isotope analysis, and quantitative realtime
polymerase chain reaction (qPCR) analysis targeting the genera Dehalococcoides and Dehalogenimonas and
the genes vcrA, bvcA, and cerA. A decade prior to this sampling campaign, the plume source was thermally
remediated by steam injection. This released dissolved organic carbon (DOC) that stimulated microbial activity
and created reduced conditions within the plume. Based on an inclusive analysis of minor and major sampling
campaigns since the initial site characterization, it was estimated that reduced conditions peaked 4 years after
the remediation event. At the time of this study, 11 years after the remediation event, the redox conditions in the
aquifer are returning to their original state. However, the DOC released from the remediated source zone
matches levels measured 3 years prior and plume conditions are still suitable for biotic reductive dechlorination.
Dehalococcoides spp., Dehalogenimonas spp., and vcrA, bvcA, and cerA reductive dehalogenase genes were detected
close to the source, and suggest that complete, biotic PCE degradation occurs here. Further downgradient,
qPCR analysis and enriched δ13C values for cis-dichloroethene (cDCE) suggest that cDCE is biodegraded in a
sulfate-reducing zone in the plume. In the most downgradient portion of the plume, lower levels of specific
degraders supported by dual C-Cl analysis indicate that the biodegradation occurs in combination with abiotic
degradation. Additionally, 16S rRNA gene amplicon sequencing shows that organizational taxonomic units
known to contain organohalide-respiring bacteria are relatively abundant throughout the plume. Hydraulic
conductivity testing was also conducted, and local degradation rates for PCE and cDCE were determined at
various locations throughout the plume. PCE degradation rates from sampling campaigns after the thermal
remediation event range from 0.11 to 0.35 yr−1. PCE and cDCE degradation rates from the second to the third
sampling campaigns ranged from 0.08 to 0.10 yr−1 and 0.01 to 0.07 yr−1, respectively. This is consistent with
cDCE as the dominant daughter product in the majority of the plume and cDCE degradation as the time-limiting
step. The extensive temporal and spatial analysis allowed for tracking the evolution of the plume and the lasting
impact of the source remediation and illustrates that the multiple lines of evidence approach is essential to
elucidate the primary degradation mechanisms in a plume of such size and complexity.
Publication type
journal article
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