Well bore boundary conditions for variably saturated ̄ow modeling

Well bore boundary conditions are incorporated in a three-dimensional ®nite element model that solves the variably saturated groundwater ̄ow equation. One-dimensional line elements, which are used to discretize the ̄ow equation along the well screen, are superimposed onto three-dimensional porous media elements. The use of line elements allows the inclusion of well bore storage e€ects, and also avoids the need of a second iteration step during the solution of the nonlinear ̄ow equation to achieve the correct head and ̄ux distribution along the well screen. Veri®cation of the formulation is done by comparing results from the numerical model to an analytical solution for pumping in an uncon®ned aquifer. Simulation of convergent±divergent ̄ow into a heterogeneous uncon®ned aquifer illustrates that the model accounts for the aquifer heterogeneity by producing a variable ̄uid ̄ux distribution along the well screen. This result has implications for the correct modeling of contaminant transport to the well. Ó 2000 Elsevier Science Ltd. All rights reserved.