Simulation of contaminant transport in fractured permeable formations by multiporosity modeling

• Published in: Journal of hydrology (Amsterdam) Vol. 223; no. 3; pp. 107 - 130
• Main Authors: Rubin, H., Jansen, D., Forkel, C., Köngeter, J.
• Format: Journal Article
• Language: English
• Published: Amsterdam Elsevier B.V 01.10.1999; Elsevier Science
• Subjects: adsorption; aquifers; diffusivity; Earth sciences; Earth, ocean, space; Engineering and environment geology. Geothermics; equations; Exact sciences and technology; Fractured formations; groundwater contamination; Hydrogeology; Hydrology. Hydrogeology; mathematical models; Multi-porosity modeling; Multiple aquifers; permeability; pollutants; Pollution, environment geology; porosity; simulation models; transport processes; Transport simulation; Transport simulation; Multi-porosity modeling; Fractured formations; Multiple aquifers; models; diffusion; density; porosity; permeability; ground water; digital simulation; transport; pollution; contamination; aquifers; diffusivity; fractures
• ISSN: 0022-1694; 1879-2707
• DOI: 10.1016/S0022-1694(99)00098-0

This paper concerns contaminant transport in aquifers comprising fractured porous formations. It is considered that the aquifer subject to contamination is composed of macro-blocks, which embed two sets of macro-fractures. Each macro-block incorporates numerous micro-blocks of low permeability, which embed micro-fractures. Therefore, the basic conceptual model, used in this study, is a triple-porosity two-dimensional model. It is shown that five dimensionless parameters govern contaminant transport in the triple-porosity domain. However, a group of eight so-called practical parameters is convenient to be used for consideration of possible scenarios. From this group, major effects of contaminant diffusion into the micro-blocks are attributed to the density of micro-fractures and porosity of the micro-blocks. Coefficient of diffusivity of contaminant into the micro-block is also a significant parameter. Its effective value increases due to the presence of vertical fractures, which do not transfer contaminant by advection, and it is dependent on the tortuosity of the micro-block material. Simulations of various possible scenarios were carried out by solving the basic dimensionless equations developed in the present study. The solutions were obtained by a combination of analytical and numerical solutions. The simulations indicate that at a comparatively high porosity of the micro-blocks, of the order 10 −1, the effect of contaminant diffusion into the micro-blocks can be approximated as a retardation phenomenon, similar to contaminant adsorption. An increase of the fracture density reduces that retardation effect. If the micro-block porosity is comparatively low, of the order 10 −3, then contaminant diffusion into the micro-blocks changes the shape of the breakthrough curves, which are ended with very long tails. This phenomenon is reduced by the increase of the fracture density.