Implementing Intrawell, Intercell Flow into Finite-Difference Ground-Water Flow Model

The U.S. Geological Survey, finite-difference flow model (MODFLOW) is the most commonly applied numerical code in ground-water hydrology. This flow model is frequently used in the design of pump-and-treat systems for aquifer remediation. In this paper we modified the MODFLOW well package to improve on the approximation of multilayer well effects when simulating vertical wells that penetrate several layers and adjacent cell effects when simulating horizontal wells. This was done by simulating flow through a well as flow through a closed conduit pipe, to incorporate flow between adjacent model cells that contain the well. Thus, water exchange between adjacent layers or cells containing the same well as dependent on the flow within the well and flow outside the well of the adjacent cells containing the well. Examples are presented involving ground-water extraction to demonstrate the applicability of the approach to simulate horizontal and vertical wells. It was proposed that the shape of the capture zone of pumping was closer to that of a pear than that of an ellipsoid.