An interpretation of potential scale dependence of the effectivematrix diffusion coefficient
Matrix diffusion is an important process for solutetransport in fractured rock, and the matrix diffusion coefficient is akey parameter for describing this process. Previous studies indicatedthat the effective matrix diffusion coefficient values, obtained from alarge number of field tracer tests, are enhanced in comparison with localvalues and may increase with test scale. In this study, we have performednumerical experiments to investigate potential mechanisms behind possiblescale-dependent behavior. The focus of the experiments is on solutetransport in flow paths having geometries consistent with percolationtheories and characterized by local flow loops formed mainly bysmall-scale fractures. The water velocity distribution through a flowpath was determined using discrete fracture network flow simulations, andsolute transport was calculated using a previously derivedimpulse-response function and a particle-tracking scheme. Values foreffective (or up-scaled) transport parameters were obtained by matchingbreakthrough curves from numerical experiments with an analyticalsolution for solute transport along a single fracture. Results indicatethat a combination of local flow loops and the associated matrixdiffusion process, together with scaling properties in flow pathgeometry, seems to be the dominant mechanism causing the observed scaledependence of theeffective matrix diffusion coefficient (at a range ofscales).
- Research Organization:
- Lawrence Berkeley National Lab. (LBNL), Berkeley, CA (United States)
- Sponsoring Organization:
- USDOE. Office of Civilian Radioactive Waste Management.Waste Management System
- DOE Contract Number:
- DE-AC02-05CH11231
- OSTI ID:
- 901047
- Report Number(s):
- LBNL-60744; JCOHE6; R&D Project: G60731; BnR: DF0961000; TRN: US200711%%773
- Journal Information:
- Journal of Contaminant Hydrology, Vol. 90, Issue 1-2; Related Information: Journal Publication Date: 02/20/2007; ISSN 0169-7722
- Country of Publication:
- United States
- Language:
- English
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