Well bore boundary conditions for variably saturated flow modeling

Well bore boundary conditions are incorporated in a three-dimensional finite element model that solves the variably saturated groundwater flow equation. One-dimensional line elements, which are used to discretize the flow 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 effects, and also avoids the need of a second iteration step during the solution of the nonlinear flow equation to achieve the correct head and flux distribution along the well screen. Verification of the formulation is done by comparing results from the numerical model to an analytical solution for pumping in an unconfined aquifer. Simulation of convergent–divergent 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 correct modeling of contaminant transport to the well.