Quantification of coupled fluid flow and reactive transport using a dissolved gas tracer test in a fractured media
Résumé
Identification of biogeochemical reactions in
aquifers and determining kinetics is important for the
prediction of contaminant transport in aquifers and
groundwater management. Therefore, experiments
accounting for both fluid flow and reactive transport
are essential to quantify reactive transport properties
at field scale.
This study presents the results of a groundwater
tracer test using the combined injection of dissolved
conservative and reactive gases (He, Xe, Ar, and O2)
and NO3
- in order to evaluate the transport properties
of a fractured media in Brittany, France.
Dissolved gas concentrations are continuously
monitored in situ with a CF-MIMS (Continuous Flow
- Membrane Inlet Mass Spectrometer) allowing a
high frequency (1 gas every 1.5 seconds) multi-tracer
analysis (N2, O2, CO2, CH4, N2O, H2, He, Ne, Ar, Kr,
Xe) over a large resolution (6 orders of magnitude).
Along with dissolved gases, groundwater
biogeochemistry are monitored through the sampling
of major anions and cations, trace elements and
microbial diversity analysis.
The results show breakthrough curves allowing
the combined quantification of conservative and
reactive transport properties such as dispersivity,
fracture aperture as well as reactions kinetic
parameters. This ongoing work consisting in the field
characterization of biogeochemical reactivity is to be
implemented in other fracture networks in order to
investigate the link between fluid flow properties and
reaction kinetics.