A SCREENING MODEL FOR NONAQUEOUS PHASE LIQUID TRANSPORT IN THE VADOSEZONE USING GREEN-AMPT AND KINEMATIC WAVE THEORY

In this paper, a screening model for flow of a nonaqueous phase liquid (NAPL) and associated chemical transport in the vadose zone is develo ped. The model is based on kinematic approximation of the governing eq uations for both the NAPL and a partitionable chemical constituent. Th e resulting governing equation is a first-order, quasi-linear hyperbol ic equation to which the generalized method of characteristics can be applied. This approach generally neglects the contribution to the NAPL flux from capillary pressure gradients. During infiltration under pon ded conditions, or when the NAPL flux exceeds the maximum effective co nductivity of the soil, the effect of capillary suction is included in the model through the usage of the Green-Ampt model. All of the resul ting model equations are in the form of ordinary differential equation s which are solved numerically by a variable time step Runge-Kutta tec hnique. Results from a simple column experiment were used to evaluate the vadose zone flow model assumptions. Independently measured paramet ers allow simulation without calibration of the model results. The mat ch of the model to the data suggests that the model captures the quali tative behavior of the experimental system and is capable of an accept able degree of quantitative agreement.