In many cases, water levels in wells are observed to fluctuate significantly in response to changes in barometric pressure. In this study, a physically based conceptual model for the influence of barometric pressure on groundwater wells was developed and tested;It is proposed that water level fluctuations in response to barometric pressure are due, in large part, to the different manner in which the pressure is propagated through the water column in the well and the porous media outside the well. Changes in pressure transmit through the water column in the well to the screened region with essentially negligible loss in pressure. On the contrary, pressure changes transferred through the porous media to the screened elevation outside the well undergo an irreversible transformation of fluid potential (head loss). Consequently, the loss in pressure head through the porous medium causes a lateral hydraulic head gradient to be developed around the well-screen region, as well as a vertical one through the porous medium. In response to the head gradient developed due to changes in barometric pressure, groundwater flows are induced through the well screen, with subsequent changes in well-casing storage. In the proposed model the well itself is an essential element. The well-water flux across the screen and the consequent change in wellcasing storage were appropriatety linked with groundwater flow in the surrounding porous medium and estimated through an iteration technique. This approach incorporates the traditional governing theories on groundwater flow: conservation of mass and Darcy's Law; Groundwater was modeled as two-dimensional (radial and vertical) unsteady flow, and solved by using finite element approximations. The basic concept of the model was successfully applied to the modeling of slug tests and furthermore it was demonstrated that a series of slug/bad tests and effects of barometric pressure on wells are theoretically related to each other in physical and numerical senses through the principle of super position;The results suggest that the physically based model in this study is very effective in estimating the water level fluctuations in a well due to changes in barometric pressure. The magnitude and behavior of the well response varies with the hydraulic properties (hydraulic conductivity and specific storage) and well geometry (casing radius, screened length, and depth of well).