Numerical Investigations of Mixing in Physically Heterogeneous Porous Media using the One- and Two-Particle Covariance

Several works have pointed out that local dispersion plays a crucial role in determining the behavior of the concentration variance and coef¿cient of variation over time for conservative tracers. Numerical investigations aimed at evaluating the effect of the local dispersivity on dilution time scales are performed using a random-walk particle-tracking method model applied to transport of conservative solutes in representations of random media. The computed oneand two-particle covariances are used to characterize solute mixing by approximating the dilution time scales and the reactor ratios of the plumes. The effect of the microdispersivity on these time scales is found to be signi¿cant, with the time scales varying in an inverse fashion to the local dispersion coef¿cients. Dilution is found to vary with the diffusion time, with the dilution time scales being on the order of tens to thousands of diffusion times.