Lagrangian simulation of multidimensional anomalous transport at the MADE site

Contaminant transport through regional-scale natural geological formations typically exhibits several anomalous'' features, including direction-dependent spreading rates, channeling along preferential flow paths, trapping of solute in relatively immobile domains, and/or the local variation of transport speed. Simulating these plume characteristics can be computationally intensive using a traditional advection-dispersion equation (ADE) because anomalous features of transport generally depend on local-scale subsurface properties. Here we develop an alternative simulation approach that solves the full nonlocal, multidimensional, spatiotemporal fractional-order ADE with variable coefficients in a Lagrangian framework using a novel non-Markovian random walk method. This model allows us to simulate anomalous plumes without the need to explicitly define local-scale heterogeneity. The simple model accurately simulates the tritium plume measured at the extensively characterized MADE test site.