Modeling Non‐Fickian Solute Transport Due to Mass Transfer and Physical Heterogeneity on Arbitrary Groundwater Velocity Fields

Abstract

AbstractWe present a hybrid approach to groundwater transport modeling, “CTRW‐on‐a‐streamline,” that allows continuous‐time random walk (CTRW) particle tracking on large‐scale, explicitly delineated heterogeneous groundwater velocity fields. The combination of a non‐Fickian transport model (in this case, the CTRW) with general heterogeneous velocity fields represents an advance of the current state of the art, in which non‐Fickian transport models or heterogeneous velocity fields are employed but generally not both. We present a general method for doing this particle tracking that fully separates the model parameters characterizing macroscopic flow, subscale advective heterogeneity, and mobile‐immobile mass transfer, such that each can be directly specified a priori from available data. The method is formalized and connections to classic CTRW and subordination approaches are made. Numerical corroboration is presented.