Communicated by J. Vigo-AguiarDiffusion processes have traditionally been modeled using the classical parabolic advection-diffusion equation. However, as in the case of tracer transport in porous media, significant discrepancies between experimental results and numerical simulations have been reported in the literature. Therefore, in order to describe such anomalous behavior, known as non-Fickian diffusion, some authors have replaced the parabolic model with the continuous time random walk model, which has been very effective. Integro-differential models (IDMs) have been also proposed to describe non-Fickian diffusion in porous media. In this paper, we introduce and test a particular type of IDM by fitting breakthrough curves resulting from laboratory tracer transport. Comparisons with the traditional advection-diffusion equation and the continuous time random walk are also presented. Moreover, we propose and numerically analyze a stable and accurate numerical procedure for the two-dimensional IDM composed by a integro-differential equation for the concentration and Darcy's law for flow. In space, it is based on the combination of mixed finite element and finite volume methods over an unstructured triangular mesh.where the total mass flux J is given by where J adv is the flux due to convective transport J adv D vu, and by assuming that the diffusion-dispersion mass flux J dis satisfies the so-called Fick's law,Equation (1), being of the parabolic type, induces a pathologic behavior in the concentration u, namely, it presents infinite speed of propagation, which has no physical meaning. Other limitations associated with the definition of D.v/ have also been reported [6][7][8].Regarding the use of such an equation to simulate tracer transport, several gaps have been observed when simulation results were compared with laboratory experiments. These observations have been extensively reviewed [9][10][11][12][13][14][15][16][17][18].Several approaches have been developed in order to overcome the limitations associated with Equation (1); we refer, for example, to [7] and [8]. A common approach consists of the introduction of a hyperbolic or non-Fickian correction term. A particular model of this type can be obtained by assuming that the diffusion-dispersion mass flux J dis satisfies the following differential equation:where is a delay parameter [19]. Note that the left-hand side of Equation (5) is a first-order approximation of the left-hand side of J dis .x, t C / D D.v/ru.x, t/, which means that the dispersion mass flux at the point x and time t C depends on the gradient of the concentration at the same point but at a delayed time. Equation (5) leads towith the kernel term K er .t/ D 1 e t , provided that J dis .0/ D 0. Combining the partition (4) with Equation (3), where J dis is given by Equation (6), we obtain the integro-differential equationMoreover, if we assume that the diffusion-dispersion mass flux has both a Fickian component J F , and a non-Fickian component J NF , defined byandThe intent of this section is...