CONTAMINANT ADVECTION AND SPREADING IN A FRACTURED PERMEABLE FORMATION .2. NUMERICAL-SIMULATION

In a companion paper, referred to as paper I, the transport of contaminants in a fractured permeable formation was characterized and formulated. It was shown that advective movements in the fracture flow and the permeable block flow, as well as mixing between these two types of flow, are the most significant factors affecting contaminant transport and spreading in such formations. The basic formulation and the closed-form analytical solution developed in paper I invite the use of numerical schemes for a further analysis of the contaminant transport processes. In the framework of the present paper this target is achieved. A numerical solution scheme stemming from the conceptual model of paper I is developed. Simulations are performed by considering the various properties of the discrete fracture flow and the permeable block flow. The results of the present study indicate that fractured permeable formations can be represented by single continuum models provided that a sufficiently large number of sectors is included in the representative elementary volume (REV). The minimum number of sectors depends on the ratio between the specific discharge of the permeable block flow and that imposed by the fracture presence. This ratio is named the mobility number. The larger the mobility number the smaller the number of sectors which should be incorporated in the REV. Equivalent properties of the continuum representing the fractured permeable formation, such as the equivalent porosity and dispersivity, are determined and evaluated.