Effective matrix diffusion in kilometer‐scale transport in fractured crystalline rock

Shapiro, Allen M.

doi:10.1029/2000wr900301

Cited by 134 publications

(144 citation statements)

References 34 publications

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“…The enhancement of the fracture (fault) -matrix interface area (or effective matrix-diffusion coefficient) seems to be common for matching field-scale solute transport observations, as suggested by this study and previous studies (Shapiro, 2001;Neretnieks, 2002;Liu et al, 2003a). Although some physical explanations for this enhancement are available, as discussed in Section 4.3, more detailed studies of the associated mechanisms are needed to confirm these explanations.…”

Section: Implication For Radionuclide Transport In the Unsaturated Zosupporting

confidence: 81%

“…They include (1) advective mass exchanges from high-permeability fractures to low-permeability fractures (Shapiro, 2001), (2) diffusion into stagnant water zones (Neretnieks, 2002), and (3) enhanced fracture-matrix interface areas for fractures with small-trace lengths that do not contribute to global flow and are not considered in the survey data (and therefore in the numerical grid) (Wu et al, 2003;Liu et al, 2003a, b). In addition to these potential mechanisms, two other factors also contribute to the increase in the interface area.…”

Section: Effects Of Matrix Diffusionmentioning

confidence: 99%

“…While effects of matrix diffusion on solute transport in saturated fractured rocks have been intensively investigated (e.g., Neretnieks, 1980Neretnieks, , 2002Moreno et al, 1997;Ostensen, 1998;Jardine et al, 1999;Shapiro, 2001;McKenna et al, 2001;Meigs and Beauheim, 2001), studies of these effects in unsaturated fractured rock are relatively limited in the literature. Compared with saturated systems, the effects of matrix diffusion in unsaturated systems are more complex, owing to the involved multiphase flow processes and the corresponding fracture-matrix interaction mechanisms.…”

Section: Introductionmentioning

confidence: 99%

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Field investigation into unsaturated flow and transport in a fault: model analyses

Liu

Salve

Wang

et al. 2004

Journal of Contaminant Hydrology

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Results of a fault test performed in the unsaturated zone of Yucca Mountain, Nevada, were analyzed using a three-dimensional numerical model. The fault was represented as a vertical fracture and the surrounding rock was treated as a dual-continuum system in the model. Model calibration against the seepage and water travel velocity data suggests that the lithophysal cavities connected to fractures can considerably enhance the effective fracture porosity and therefore retard water flow in fractures. Comparisons between simulation results and the tracer concentration data also indicate that the matrix diffusion is an important mechanism for solute transport in unsaturated fractured rock. We found that an increased fault-matrix interface area was needed for matching the observed tracer data, which is consistent with previous studies. The study results suggest that the current site-scale model for the unsaturated zone of Yucca Mountain may underestimate radionuclide transport time within the unsaturated zone, because effects of an increased fracture-matrix interface area and the lithophysal cavities are not considered in the current site-scale model.2

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Section: Implication For Radionuclide Transport In the Unsaturated Zosupporting

confidence: 81%

Section: Effects Of Matrix Diffusionmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

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Field investigation into unsaturated flow and transport in a fault: model analyses

Liu

Salve

Wang

et al. 2004

Journal of Contaminant Hydrology

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“…This study differs from previous studies in that it involved multiple tracer transport and therefore allowed for a direct demonstration of the importance of matrix diffusion through unsaturated fractured rock. Compared with saturated systems [e.g., Neretnieks, 1980Neretnieks, , 2002Moreno et al, 1997;Jardine et al, 1999;Shapiro, 2001;Reimus et al, 2003], the effects of matrix diffusion in unsaturated systems are more complex, owing to the multiphase flow processes involved and the corresponding fracture-matrix interaction mechanisms.…”

Section: Matrix Diffusionmentioning

confidence: 99%

“…However, while several field studies have investigated matrix diffusion processes in saturated fractured rock [e.g., Albelin et al, 1991;Novakowski and Lapcevic, 1994;Hadermann and Heer, 1996;Jardine et al, 1999;Callahan et al, 2000;Shapiro, 2001;Reimus et al, 2003], very few field studies have investigated these processes in unsaturated fractured rock environments [e.g., Hu et al, 2001].…”

Section: Introductionmentioning

confidence: 99%

Unsaturated flow and transport through a fault embedded in fractured welded tuff

Salve

Liu

Cook

et al. 2004

Water Resources Research

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[1] To evaluate the importance of matrix diffusion as a mechanism for retarding radionuclide transport in the vicinity of a fault located in unsaturated fractured rock, we carried out an in situ field experiment in the Exploratory Studies Facility at Yucca Mountain, Nevada. This experiment involved the release of $82,000 L of water over a period of 17 months directly into a near-vertical fault under both constant positive head (at $0.04 m) and decreasing fluxes. A mix of conservative tracers (pentafluorobenzoic acid (PFBA) and bromide (applied in the form of lithium bromide)) was released along the fault over a period of 9 days, 7 months after the start of water release along the fault. As water was released into the fault, seepage rates were monitored in a large cavity excavated below the test bed. After the release of tracers, seepage water was continuously collected from three locations and analyzed for the injected tracers. Observations of bromide concentrations in seepage water during the early stages of the experiment and bromide and PFBA concentrations in the seepage water indicate the significant effects of matrix diffusion on transport through a fault embedded in fractured, welded rock.

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Influence of porosity structures on mixing-induced reactivity at chemical equilibrium in mobile/immobile Multi-Rate Mass Transfer (MRMT) and Multiple INteracting Continua (MINC) models

et al. 2013

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[1] Trapping mechanisms and slow diffusion in poorly connected porosities are well modeled by several anomalous transport models including the Multi-Rate Mass Transfer framework (MRMT). In MRMT, solutes in fast mobile advective zones are slowed down by first-order exchanges with immobile zones. While MRMT models have been used essentially for conservative transport, we investigate their relevance to reactive transport.To this end, we analyze the influence of the structure of the diffusive porosity zone on the distribution of concentrations within the immobile zone and on the reactivity of simple precipitation/dissolution bimolecular reactions at equilibrium. We build Multi-Rate Mass Transfer (MRMT) and Multiple INteracting Continua (MINC) models with equivalent transport characteristics. Both models have the same mobile zone concentrations at any time. They, however, differ by the connectivity structure of their immobile zones. MRMT has a star-shaped connectivity structure with the mobile zone linked to all immobile zones and acting as the sole exchanger. MINC has a chained-type connectivity where immobile zones are mutually connected on a line. We show that both connectivity structures give the same concentration variance whatever the model parameters, dimensionality, and initial conditions. Reaction rates of bimolecular reaction at chemical equilibrium are also highly similar but not equal as long as concentration gradients within the diffusive zone remain low like in the uniform injection case, or at large times when high initial concentration gradients have been reduced. For high initial immobile concentration gradients in the diffusive zone, however, reaction rates are much lower in the star-shaped connectivity structure (MRMT), and consequently depend on the organization of the immobile porosity structure. Negative concentrations also occur in some of the immobile zones of the equivalent MRMT as a result of the direct connection of the mobile and immobile zones. While acceptable for conservative components, negative concentrations limit the relevance of MRMT to model reactivity at high immobile concentration gradients. The concept of immobile zone concentration should thus be taken with great care and systematically be assessed.

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Effective matrix diffusion in kilometer‐scale transport in fractured crystalline rock

Cited by 134 publications

References 34 publications

Field investigation into unsaturated flow and transport in a fault: model analyses

Field investigation into unsaturated flow and transport in a fault: model analyses

Unsaturated flow and transport through a fault embedded in fractured welded tuff

Influence of porosity structures on mixing-induced reactivity at chemical equilibrium in mobile/immobile Multi-Rate Mass Transfer (MRMT) and Multiple INteracting Continua (MINC) models

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