Development of a Continuous Time Random Walk Model for Fractured Media - Site Characterization and Comparison with Discrete Fracture Network Method
AuthorPickman, Luke Hunter
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Due to the difficulties in accurately modeling particle movement in fractured geologic media, non-local contaminant transport methods have been extensively studied as an alternative to the classic Advection Dispersion Equation. The Discrete Fracture Network (DFN) model successfully produces plume evolution at shorter distances by synthetically generating a fracture network based on known fracture characteristics and conducting flow and particle tracking simulations. Due to the computational complexities to run such a model, it is difficult to apply this approach at larger scales. The Continuous Time Random Walk (CTRW) method provides a framework for modeling non-Fickian transport through fracture networks by employing probability distributions to generate particle jump lengths and residence times spanning multiple orders of magnitude. By analyzing borehole data, characteristics of the fracture network are used to extract salient information for use in construction of site-representative DFN realizations. Through characterization and proper assignment of both particle travel time and fracture length distributions, a continuous time random walk model is constructed to predict migration of non-reactive particles on a continuum of spatial and temporal scales. The predictions are compared against DFN results to determine the future viability of using CTRW as an upscaling technique for particle transport through fractured media.