title: Tracer diffusion from a horizontal fracture into the surrounding matrix: measurement by computed tomography.
abstract: The vertical diffusion of NaI solution from a horizontal fracture into and within the surrounding matrix was tracked and quantified over time using an artificially fractured chalk core (30x5 cm) and a second-generation X-ray computed tomography (CT) scanner. The different tracer-penetration distances imaged in the matrix above and below the horizontal fracture are indicative of a greater tracer mass penetrating into the lower matrix. The enhanced transport in the matrix below the fracture was related to the Rayleigh-Darcy instability induced by the density differences between the heavier tracer solution in the fracture (1.038) and the distilled water that had initially resided in the matrix. Our observations suggest that below the fracture, the tracer is propagated by an advection-diffusion process that is characterized by both higher rates and higher concentrations relative to its propagation by diffusion above the fracture. The experimental results suggest that the prediction of contaminant migration in a rock intersected by both vertical and horizontal (e.g. along bedding planes) fractures is difficult because of density effects that result in different solute-penetration rates.
authors: The Seagram Center for Soil and Water Sciences, Faculty of Agricultural, Food and Environmental Quality Sciences, The Hebrew University of Jerusalem, PO Box 12, Rehovot 76100, Israel.
authors: Amir
authors: A
authors: Polak
authors: Abraham S
authors: AS
authors: Grader
authors: Rony
authors: R
authors: Wallach
authors: Ronit
authors: R
authors: Nativ
mesh_terms: D004058:Diffusion; D004784:Environmental Monitoring / Q000379:methods; D005544:Forecasting; D055593:Geological Phenomena; D005844:Geology; D008962:Models, Theoretical; D012987:Soil; D012989:Soil Pollutants; D014057:Tomography, X-Ray Computed; D014873:Water Pollutants
chemical_list: D012987:Soil; D012989:Soil Pollutants; D014873:Water Pollutants