Well bore boundary conditions for variably saturated flow modeling

Well bore boundary conditions are incorporated in a three-dimensional finit e element model that solves the variably saturated groundwater flow equatio n. One-dimensional line elements, which are used to discretize the flow equ ation along the well screen, are superimposed onto three-dimensional porous media elements. The use of line elements allows the inclusion of well bore storage effects, and also avoids the need of a second iteration step durin g the solution of the nonlinear flow equation to achieve the correct head a nd flux distribution along the well screen. Verification of the formulation is done by comparing results from the numerical model to an analytical sol ution for pumping in an unconfined aquifer. Simulation of convergent-diverg ent flow into a heterogeneous unconfined aquifer illustrates that the model accounts for the aquifer heterogeneity by producing a variable fluid flux distribution along the well screen. This result has implications for the co rrect modeling of contaminant transport to the well. (C) 2000 Elsevier Scie nce Ltd. All rights reserved.