Ground Water Flow Modeling in a Layered Sedimentary Fractured Media Aquifer System using MODFLOW with the PMF Package

Ground water movement in fractured media is markedly different from that in porous media. This difference can be summarized as a continuous change of flow properties in porous media as opposed to a discrete change of flow properties in fractured media. Therefore, the direct use of MODFLOW, which was originally developed to simulate porous media systems, to model fractured media systems is quite limited. Indeed, a special characteristic of ground water movement in fractured media, namely preferred fluid pathways, is difficult to simulate in a finite difference model such as MODFLOW. In order to define this preferred fluid pathway, the model domain should have several different categories of cells such that one would represent densely fractured areas while the others represent sparsely fractured areas in the model domain. We developed the PMF package (a Preprocessor to MODFLOW for Fractured media) using percolation theory in order to allow the model domain of MODFLOW to show preferred fluid pathways composed of fracture connections. The layered sedimentary fractured media located in Piscataway, NJ, was simulated by MODFLOW with the PMF package in this study. Its hydrogeological structure consists of a water bearing unit having a dense fracture distribution and a confining unit having a sparse fracture distribution. Ground water flows mostly through the connected fractures in the water bearing units, which can be considered to be the preferred fluid pathway. The PMF package allowed the model domain to show these two different units by the distribution of two different types of cells and produced a simulation having better fits to observation data and a better agreement with the geological characteristics of system than simulations performed by MODFLOW alone. We can conclude that the application of the PMF package to a layered sedimentary fractured aquifer to simulate ground water flow yielded superior results, as its application also provided better results in a crystalline fractured aquifer in a previous study.