EGU2020-9709, updated on 10 Jan 2024
https://doi.org/10.5194/egusphere-egu2020-9709
EGU General Assembly 2020
© Author(s) 2024. This work is distributed under
the Creative Commons Attribution 4.0 License.

Inferring high-resolution aquifer hydraulic conductivity and groundwater fluxes by active heat tracer using direct push fiber optics

Cynthia Lee1, Olivier Bour2, Jean-Marc Ballard1, Nataline Simon2, Jerome de la Bernardie2, Daniel Paradis3, Jasmin Raymond1, and Rene Lefebvre1
Cynthia Lee et al.
  • 1INRS, Centre Eau Terre Environnement, Quebec, Canada (rene.lefebvre@ete.inrs.ca)
  • 2Géosciences Rennes, UMR 6118, Université de Rennes & CNRS, Rennes, France (olivier.bour@univ-rennes1.fr)
  • 3Geological Survey of Canada, Natural Resources Canada, Quebec, Canada (daniel.paradis@canada.ca)
Characterizing aquifer heterogeneity for contaminant transport prediction remains a challenge in subsurface hydrology. In recent years, fiber optics (FO) Distributed Temperature Sensing (DTS) has enabled the study of transient hydrogeological processes with high spatial and temporal resolutions. Recent studies have shown that vertical profiles of groundwater fluxes can be quantified in granular aquifers through inversion of the thermal responses from active heat tracer tests using FO cables installed by direct push. Here, we further investigate the potential of active FO-DTS methods for granular aquifer characterization by performing a multiscale characterization and active heat tracer experiment in a well-characterized heterogeneous deltaic aquifer located north of Quebec City, Canada. This aquifer has been the object of detailed hydrogeological characterization and thus provides a wide range of existing data. In particular, we will test whether the vertical distribution of groundwater fluxes in the sub-surface determined by these inversions can be used to estimate hydraulic properties at a spatial scale that can be used to assess the impact of aquifer heterogeneity on mass transport and dispersion. 
This communication focuses on a site where two FO cables were installed 10 m apart by direct push. An active heat tracer experiment was carried out with the two FO cables, and the resulting thermal responses were inverted to obtain high-resolution vertical profiles of the groundwater fluxes at each FO cable. Heating was carried out in the saturated zone, between depths of 12 to 40 m with a 25-cm vertical sampling. Using data from a piezometric survey, the groundwater fluxes from the FO-DTS were used to estimate a range of hydraulic conductivities (K). A previous study at the field site has shown that cone penetration test (CPT) profiles can be used to recognize the different hydrofacies with distinct ranges of hydraulic conductivity present in the deltaic aquifer. As the two FO cables were co-located with a previously done CPT profile, the measured fluxes and estimated K values could be compared to known ranges of K. 
Results show quite varying temperature profiles and accordingly distinct groundwater fluxes. These varying fluxes are coherently correlated to the different hydrofacies identified with the co-located CPT responses at a similar vertical scale. The two FO-DTS temperature profiles are also quite similar when considering the small variations in hydrofacies found along their length. These results show that FO-DTS heat tracer tests provide consistent and representative measurements of groundwater fluxes in agreement with the heterogeneous distribution of K as indicated by CPT. Thus, compared with existing hydraulic methods, FO-DTS heat tracer tests provide new and complementary data that have a great potential for characterizing solute transport in granular aquifers with a high spatial resolution.

How to cite: Lee, C., Bour, O., Ballard, J.-M., Simon, N., de la Bernardie, J., Paradis, D., Raymond, J., and Lefebvre, R.: Inferring high-resolution aquifer hydraulic conductivity and groundwater fluxes by active heat tracer using direct push fiber optics, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-9709, https://doi.org/10.5194/egusphere-egu2020-9709, 2020.

This abstract will not be presented.