Modeling soil vapor extraction employing dual flow network

Rebounding and tailing are related phenomena that have been observed in soil vapor extraction (SVE). Because tailing lengthens SVE clean-up times significantly, there exists a need to model the soil in a manner that explains tailing as well as the associated rebounding of contaminant concentration that occurs after a SVE shut off period. Additionally, modeling the influence of fracturing soil, which is done to improve contaminant recovery in low permeability soil, has yet to be modeled in the literature. To model tailing and the related rebounding, as well as the influence of fracturing to improve SVE in low permeability soil, this paper uses a dual flow network soil conception. Partitioning of the contaminants from the gas to liquid phase is modeled with equilibrium reactions. The partitioning from gas to sorbed phase is modeled with a both equilibrium and kinetic reaction. The finite element method is used to solve the mass balance equations that occur in gas flow and transport in space. The finite difference method is used to model the time terms. The results of the modeling show that a dual flow network conception can reproduce the rebounding and tailing effect. A one-dimensional model illustrates rebounding and tailing. Reproduction of one-dimensional laboratory soil column data illustrates the models ability to simulate laboratory column data and calibrate the exchange terms. The improved removal of contaminants and vapor flow rates due to fracturing is illustrated with a two-dimensional dual flow network model. Dual flow network modeling shows promise in simulating rebounding, tailing, and the influence of fracturing in SVE. However, an experimental program designed to fulfill the data requirements of the model is needed to rigorously evaluate these systems and dual flow network's capability of simulating real data.