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| Titel |
Probabilistic Health Risk Assessment of Chemical Mixtures: Importance of Travel Times and Connectivity |
| VerfasserIn |
Christopher V. Henri, Daniel Fernàndez-Garcia, Felipe P. J. de Barros |
| Konferenz |
EGU General Assembly 2014
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| Medientyp |
Artikel
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| Sprache |
Englisch
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| Digitales Dokument |
PDF |
| Erschienen |
In: GRA - Volume 16 (2014) |
| Datensatznummer |
250093145
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| Publikation (Nr.) |
 EGU/EGU2014-7606.pdf |
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| Zusammenfassung |
| Subsurface contamination cases giving rise to groundwater pollutions are extensively found
in all industrialized countries. Under this pressure, risk assessment methods play an important
role in population protection by (1) quantifying the potential impact on human health of an
aquifer contamination and (2) helping and driving decisions of groundwater-resource
managers.
Many reactive components such as chlorinated solvents or nitrates potentially experience
attenuation processes under common geochemical conditions. This represents an attractive
and extensively used remediation solution but leads often to the production of by-products
before to reach a harmless chemical form. This renders mixtures of contaminants a common
issue for groundwater resources managers. In this case, the threat posed by these
contaminants to human health at a given sensitive location greatly depends on the
competition between reactive and advective-dispersive characteristic times. However,
hydraulic properties of the aquifer are known to be spatially variable, which can lead to the
formation of preferential flow channels and fast contamination pathways. Therefore, the
uncertainty on the spatial distribution of the aquifer properties controlling the plume travel
time may then play a particular role in the human health risk assessment of chemical
mixtures.
We investigate here the risk related to a multispecies system in response to different
degrees of heterogeneity of the hydraulic conductivity (K or Y =ln(K)).
This work focuses on a Perchloroethylene (PCE) contamination problem followed by the
sequential first-order production/biodegradation of its daughter species Trichloroethylene
(TCE), Dichloroethylene (DCE) and Vinyl Chlorine (VC). For this specific case, VC is
known to be a highly toxic contaminant. By performing numerical experiments, we evaluate
transport through three-dimensional mildly (ÏăY 2=1.0) and highly (ÏăY 2=4.0) heterogeneous
aquifers. Uncertainty on the hydraulic conductivity field is considered through a Monte Carlo
scheme, and statistics of the total risk for human health (RT) related to the mixtures of the
four carcinogenic plumes are evaluated.
Results show two distinct spatiotemporal behavior of the RT estimation. Simulations in
highly heterogeneous aquifers display a lower mean of RT close to the injection and higher
further away. We explain this by the distinct ranges of travel times and connectivity metrics
related to the two sets of aquifers. A high ÏăY 2 trends to decrease the travel time (and
increase the connectivity). Early travel times, associated to channeling effects, are
intuitively perceived as an indicator for high risk. However, in our case, early travel
times lead a limited production of highly toxic daughter species and a lower total
risk.
Our results reflect then the interplay between the characteristic reactive time for each
component and the characteristic travel time of the plume since the production of VC
depends on these factors. |
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