Unravelling long-term source removal effects and chlorinated methanes natural attenuation processes by C and Cl stable isotopic patterns at a complex field site
Author(s)
Rodríguez-Fernández, Diana
Torrentó, Clara
Palau, Jordi
Marchesi, Massimo
Soler, Albert
Domenèch, Christina
Rosell, Monica
Date issued
June 2018
In
Science of the Total Environment
No
645
From page
286
To page
296
Subjects
Carbon tetrachloride Chloroform 2D-CSIA Case study Òdena site
Abstract
The effects of contaminant sources removal in 2005 (i.e. barrels, tank, pit andwastewater pipe sources) on carbon
tetrachloride (CT) and chloroform (CF) concentration in groundwater were assessed at several areas of a fractured
multi-contaminant aquifer (Òdena, Spain) over a long-term period (2010–2014). Changes in redox conditions,
in these chlorinated methanes (CMs) concentration and in their carbon isotopic compositions (δ13C) were
monitored inmultilevelwells. δ13C values fromthese wellswere compared to those obtained fromsources (barrels,
tank and pit before their removal, 2002–2005) and to commercial solvents values in literature. Additionally,
CMs natural attenuation processes were identified by C-Cl isotope slopes (Λ).
Analyses revealed the downstreammigration of the pollutant focus and an efficient removal of DNAPLs in the pit
source's influence area. However, the removal of the contaminated soil from former tank and wastewater pipe
was incomplete as leaching from unsaturated zone was proved, evidencing these areas are still active sources.
Nevertheless, significant CMs degradation was detected close to all sources and Λ values pointed to different reactions.
For CT in the tank area, Λ value fitted with hydrogenolysis pathway although other possible reduction
processes were also uncovered. Near the wastewater pipe area, CT thiolytic reduction combined with
hydrogenolysis was derived. The highest CT degradation extent accounted for these areas was 72 ± 11% and
84±6%, respectively. For CF, the Λ value in the pit source's areawas consistentwith oxidation and/orwith transport
of CF affected by alkaline hydrolysis from upstream interception trenches. In contrast, isotope data evidenced CF reduction in the tank and wastewater pipe influence areas, although the observed Λ slightly deviates
from the reference values, likely due to the continuous leaching of CF degraded in the non-saturated zone by
a mechanism different from reduction.
tetrachloride (CT) and chloroform (CF) concentration in groundwater were assessed at several areas of a fractured
multi-contaminant aquifer (Òdena, Spain) over a long-term period (2010–2014). Changes in redox conditions,
in these chlorinated methanes (CMs) concentration and in their carbon isotopic compositions (δ13C) were
monitored inmultilevelwells. δ13C values fromthese wellswere compared to those obtained fromsources (barrels,
tank and pit before their removal, 2002–2005) and to commercial solvents values in literature. Additionally,
CMs natural attenuation processes were identified by C-Cl isotope slopes (Λ).
Analyses revealed the downstreammigration of the pollutant focus and an efficient removal of DNAPLs in the pit
source's influence area. However, the removal of the contaminated soil from former tank and wastewater pipe
was incomplete as leaching from unsaturated zone was proved, evidencing these areas are still active sources.
Nevertheless, significant CMs degradation was detected close to all sources and Λ values pointed to different reactions.
For CT in the tank area, Λ value fitted with hydrogenolysis pathway although other possible reduction
processes were also uncovered. Near the wastewater pipe area, CT thiolytic reduction combined with
hydrogenolysis was derived. The highest CT degradation extent accounted for these areas was 72 ± 11% and
84±6%, respectively. For CF, the Λ value in the pit source's areawas consistentwith oxidation and/orwith transport
of CF affected by alkaline hydrolysis from upstream interception trenches. In contrast, isotope data evidenced CF reduction in the tank and wastewater pipe influence areas, although the observed Λ slightly deviates
from the reference values, likely due to the continuous leaching of CF degraded in the non-saturated zone by
a mechanism different from reduction.
Publication type
journal article
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