Task 8.1: Gas tracing
In-situ and high-frequency measurement of dissolved gases (O2, N2, H2, Ar, Ne, He, Xe, Kr, CH4, CO2, N2O) in waters: physic of the flows and biogeochemical reactivity
The Work Package 8.1 concerning “Dissolved Gas” is based on the development of in situ measurements of dissolved gases in groundwater and surface water. These tracers allow to calculate the physical parameters of water recharge (noble gases Ne, Ar, He, Xe, Kr), to estimate water biogeochemical reactivity by measuring O2, CO2, CH4 , H2, N2O, and N2 concentrations, and lastly to estimate the water residence time in natural environments (subsoil, lakes, rivers) by helium age (4He).
The innovative measuring instrument development must meet the following criteria:
– High frequency of analysis (1 measurements per second / minute)
– Long-term measurement (a few days to a few weeks / month)
– In situ measurements in boreholes (100m) and in surface waters
– Measurement stability over time
– Equivalent precision to laboratory measurements
– Regular on-site calibrations
The technical choice was based on mass spectrometry (Figure 1), which makes it possible to identify a gaseous compound by its molar mass, coupled to a diffusion membrane, which makes it possible to continuously extract the gases from water (1 measurement per second!).
Improved equipment for hydrogeology
Hiden Analytical Company has responded to our need by optimizing the extraction membrane choice and by improving equipment robustness for its use on the field (resistance to shocks and vibrations). The equipment acquired is a “Membrane Inlet Mass Spectrometer – MIMS” (Figure 2). This equipment, already present in the oceanography domain (Tortell et al., 2005), has therefore been configured for our hydrogeological needs.
Technical development and validation of dosing procedures
The technical development and validation of the assay procedures are carried out within the framework of Eliot Chatton PhD (Figure 2). The difficulty lies in the correct calibration of each gas, which sometimes interferes with their mass (CO2 = N2O in molar mass). This development was based on the know-how of OSUR CONDATE-EAU Platform in Rennes, which for 13 years has been developing methods for measuring dissolved gases in groundwater (https://condate-eau.univ-rennes1.fr/).
Experiences on site 2015-2016
- Gaseous and heat tracing between boreholes on Ploemeur H + hydrogeological site (J Bondet of Bernardie and Eliot Chatton PhDs) – Figure 4
- Conservative and reactive tracing between drillings as part of the “Stock en Socle” Project – Eliot Chatton’s PhD
- Production of dissolved gas profiles in drilling at the Ploemeur and Betton H + site – Eliot Chatton’s PhD (Figure 3).
- Multi-gas tracing at the Beaulieu site to identify the geological parameters of the environment (permeability, porosity, transmissivity)
- Reactive and conservative tracing in the river (ZA Pleines-Fougères)
Unique in France…
Thus, CRITEX project enabled the acquisition and development of a unique and innovative instrument in France for the analysis of dissolved gases in water. This tool will undoubtedly be at the origin of numerous scientific publications and will improve knowledge in hydrogeology.
- Field continuous measurement of dissolved gases with a CF-MIMS: Applications to the physics and biogeochemistry of groundwater flow • Eliot Chatton, Thierry Labasque, Jérôme de La Bernardie, Nicolas Guihéneuf, Olivier Bour, and Luc Aquilina • Environ. Sci. Technol., Just Accepted Manuscript • DOI: 10.1021/acs.est.6b03706 • Publication Date (Web): 12 Dec 2016
Real time in situ dissolved gases monitoring in groundwater by CF-MIMS for hydrogeology , Labasque T, Chatton E, Aquilina L (Flash oral presentation et Poster)
Quantification of coupled fluid flow and reactive transport using a dissolved gas tracer tests in a fractured media, Chatton E, de La Bernardie J, Boisson A, Labasque T, Guillou A, Koch F, Aquilina L (Poster)
Real time in situ dissolved gases monitoring in groundwater by CF-MIMS for hydrogeology , Labasque T, Chatton E, Aquilina L
Mesure en continu et in situ des gaz dissous pour l’étude de la zone critique, Chatton E, Labasque T, Aquilina L
WP leader: Luc Aquilina, Thierry Labasque