Contribution of the finite volume point dilution method for measurement of groundwater fluxes in a fractured aquifer

P. Jamin (1) , Pascal Goderniaux (2) , Olivier Bour (2) , Tanguy Le Borgne (2) , A. Englert (3) , Laurent Longuevergne (2) , S. Brouyère (1)

1 Université de Liège
2 GR - Géosciences Rennes
3 Ruhr-Universität Bochum [Bochum]

Measurement of groundwater fluxes is the basis of all hydrogeological study, from hydraulics characterization to the most advanced reactive transport modelling. Usual groundwater fluxes estimation with Darcy's law may lead to cumulated errors on spatial variability, especially in fractured aquifers where local direct measurement of groundwater fluxes becomes necessary. In the present study, both classical Point Dilution Method (PDM) and Finite Volume Point Dilution Method (FVPDM) are compared on the fractured crystalline aquifer of Ploemeur, France. The manipulation includes the first use of the FVPDM in a fractured aquifer using a double packer. This configuration limits the vertical extend of the tested zone to target a precise fracture zone of the aquifer. The result of this experiment is a continuous monitoring of groundwater fluxes that lasted for more than 4 days. Measurements of groundwater flow rate in the fracture (Qt) by PDM provide good estimates only if the mixing volume (Vw) (volume of water in which the tracer is mixed) is precisely known. Conversely, the FVPDM allows for an independent estimation of Vw and Qt, leading to better precision in case of complex experimental setup such as the one used. The precision of a PDM does not rely on the duration of the experiment while a FVPDM may require long experimental duration to guarantees a good precision. Classical PDM should then be used for rapid estimation of groundwater flux using simple experimental setup. On the other hand, the FVPDM is a more precise method that has a great potential for development but may require longer duration experiment to achieve a good precision if the groundwater fluxes investigated are low and/or the mixing volume is large.

Keywords: Finite volume point dilution method; Groundwater flux; Uncertainty analysis; Double packer; Single-well tracer test; Fractured aquifer

Domains: Sciences of the Universe [physics]; Earth Sciences; Hydrology

P. Jamin, Pascal Goderniaux, Olivier Bour, Tanguy Le Borgne, A. Englert, et al.. Contribution of the finite volume point dilution method for measurement of groundwater fluxes in a fractured aquifer. Journal of Contaminant Hydrology, 2015, 182, pp.244-255. ⟨10.1016/j.jconhyd.2015.09.002⟩. ⟨insu-01200777⟩