Effect of soil layering on NAPL removal behavior in soil-heated vapor extraction

The TEVES (Thermal Enhanced Vapor Extraction System) Project is a demonstration of a process designed to extract solvents and chemicals contained in the Chemical Waste Landfill at Sandia National Laboratories. In this process, the ground is electrically heated, and borehole(s) within the heated zone are maintained at a vacuum to draw air and evaporated contaminants into the borehole and a subsequent treatment facility. TOUGH2 simulations have been performed to evaluate the fluid flow and heat transfer behavior of the system. The TOUGH2 version used in this study includes air, water, and a single-component non-aqueous phase liquid (NAPL). In the present simulations, an initial o-xylene inventory is assumed in the heated zone for illustration purposes. Variation in borehole (vapor extraction) vacuum, borehole location, and soil permeability were investigated. Simulations indicate that the temperatures in the soil are relatively insensitive to the magnitude of the borehole vacuum or the borehole locations. In contrast, however, the NAPL and liquid water saturation distributions are sensitive to these borehole parameters. As the borehole vacuum and air flow rate through the soil decrease, the possibility of contaminant (NAPL) migration from the heated zone into the surrounding unheated soil increases. The borehole location can also affect the likelihood of contaminant movement into the unheated soil.

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S.W. Webb

Papers

TOUGH2 simulations of the TEVES Project including the behavior of a single-component NAPL