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.