The main goal of this paper is to provide an approach to model the recovery of free-phase (mobile) NAPL. Based on the simplified assumptions of a so-called "sharp interface model" and vertical equilibrium between the two immiscible mobile phases (i.e. NAPL/Water), a simplified mathematical method to model the generated coupled flow of the two immiscible fluid layers during the NAPL recovery is presented. The simplified assumptions allow the introduction of potential functions for a mathematical representation of the coupled flow that satisfy partial differential equations with coupling conditions on the interface between two horizontal immiscible fluids. Based on this model, analytical and numerical solutions are presented to calculate the discharge rate of recovery systems and the location of the interface when the two immiscible components (LNAPL/Water or DNAPL/Water) are pumped out of the ground, either together or separately. The proposed method can be used as an effective tool and a benchmark solution for designing clean-up plants consisting of several wells or a trench with finite length and as a first step for the calibration of the more complex models and numerical solutions as well.
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