A quasi‐linear theory of non‐Fickian and Fickian subsurface dispersion: 2. Application to anisotropic media and the Borden site

When the quasi‐linear theory developed in paper 1 is applied to anisotropic media it shows, in contrast to the isotropic case, that longitudinal and transverse dispersivities may become asymptotically proportional to σ_Y when the log hydraulic conductivity variance σ_Y² is much smaller than 1. It further implies, among other phenomena, that when the mean seepage velocity vector μ is at an angle to the principal axes of statistical anisotropy, the long axis of a plume is generally offset toward the direction of the largest log hydraulic conductivity correlation scale; when μ is at 45° to the bedding in strongly stratified media, the longitudinal axis is nearly parallel to the bedding under non‐Fickian conditions. As Fickian conditions are approached, the plume rotates toward μ and stabilizes asymptotically at a relatively small angle of deflection depending on σ_Y². Application of the quasi‐linear theory to depth‐averaged concentration data from a tracer experiment at Borden, Ontario, yields a consistent and improved fit to a two‐dimensional model without any need for parameter adjustment. Three‐dimensional models are shown to be in fundamental conflict with observed behavior at Borden and in other stratified formations; we show that, in principle, this conflict is easy to resolve by accounting for local hydraulic anisotropy.