HR: 17:45h
AN: H14C-07    [Abstracts]
TI: Solute transport in a synthetic fracture with one porous wall: fracture-matrix interaction
AU: Michel, L
EM: laure.michel@univ-rennes1.fr
AF: Geosciences Rennes, Université Rennes 1 Campus de Beaulieu Bât. 14B, Rennes, 35042, France
AU: * Meheust, Y
EM: yves.meheust@univ-rennes1.fr
AF: Geosciences Rennes, Université Rennes 1 Campus de Beaulieu Bât. 14B, Rennes, 35042, France
AU: Caudal, J
EM: jean-pierre.caudal@univ-rennes1.fr
AF: Geosciences Rennes, Université Rennes 1 Campus de Beaulieu Bât. 14B, Rennes, 35042, France
AU: de Bremond d'Ars, J
EM: bremond@univ-rennes1.fr
AF: Geosciences Rennes, Université Rennes 1 Campus de Beaulieu Bât. 14B, Rennes, 35042, France
AU: de Dreuzy, J
EM: aupepin@univ-rennes1.fr
AF: Geosciences Rennes, Université Rennes 1 Campus de Beaulieu Bât. 14B, Rennes, 35042, France
AU: Davy, P
EM: philippe.davy@univ-rennes1.fr
AF: Geosciences Rennes, Université Rennes 1 Campus de Beaulieu Bât. 14B, Rennes, 35042, France
AB: Contaminant transport in heterogeneous fractured aquifers occurs mostly through the networks of intersecting fractures. The physical mechanisms of solute transport in a single fracture with impermeable walls are well identified (Dronfield and Silliman 1993; Roux, Plouraboué et al. 1998; Keller, Roberts et al. 1999; Detwiler and Rajaram 2000): advection, Taylor-Aris dispersion, roughness dispersion, aperture-variation dispersion and molecular diffusion. However, when the permeability of the surrounding rock matrix cannot be neglected, there is, to our knowledge, no fundamental description of the mass transfert coefficient between the region of high permeability (the fracture) and that of low permeability (the surrounding matrix). We address here solute transport through a synthetic fracture with a porous wall. We present an analog experimental model setup in which we can focus on specific dispersion mechanisms, neglecting molecular diffusion, in order to extract descriptive laws that will be integrated in future numerical models. The planar horizontal fracture is 1 m long, 5 cm wide and its mean aperture is 5 mm. It is bounded by either two smooth parallel Plexiglass plates (impermeable walls configuration), or by one such plate and a porous medium consisting of 1 mm glass beads ("semi-permeable" configuration). A permanent laminar water flow is forced through the fracture at controlled mean velocity (~ 1mm/s), and a dye (patent blue) injection system simulates a point source of contaminant along the center plane of the fracture. The tracer plume is tracked using a visualization system based on (i) lasers illuminating a series of vertical linear optical sensor arrays, and (ii) 4 cameras positioned side by side and providing a composite image of the fracture viewed from the side. The two measurement systems yield consistent quantitative temporal descriptions of the tracer concentration, integrated over the fracture width and at several positions along the fracture length. The setup was validated by checking the conservation of the total dye quantity in the impermeable walls configuration, with comparison to classical advection-dispersion models (for different injection modes). The semi-permeable configuration was then investigated. Mass transfer between the fracture and the bounding porous matrix was measured, for various concentrations of the injected dye and with different geometries (roughness) of the fracture-matrix interface. Changing the overall flow rate allowed investigation of gravity effects, which are generally disregarded in theoretical studies. As recently suggested by Polak, Grader et al. (2003), they were observed to be significant. References: Detwiler, R. L. and H. Rajaram (2000), Water Resour.Res. 36(7):1611-1625 -- Dronfield, D. G. and S. E. Silliman (1993), Water Resour.Res. 29(10):3477-3483 -- Keller, A. A., P. V. Roberts, et al. (1999), Water Resour.Res. 35(1):55-63 -- Polak, A., A. S. Grader, et al. (2003), Hydrology 67:95-112 -- Roux, S., F. Plouraboué, et al. (1998), Transport in Porous Media 32: 97-116.
DE: 1832 Groundwater transport
DE: 5104 Fracture and flow
SC: Hydrology [H]
MN: 2007 Fall Meeting