Steam flooding is used for removal of volatile organic contaminants (VOCs) from concentrated source zones. The application of steam flooding to shallow vadose zone sites can be problematic if the steam or contaminants vent to the ground surface. Cold air injection holds promise as a technique for controlling the vertical movement of the injected steam. A series of two-dimensional numerical simulations using a radially symmetric grid show the sensitivity of this process to geological and operational parameters. Air control of vertical steam movement appears to be a useful technique, using approximately equal air and steam volumetric flow rates. Air injection is shown to be more effective than a low-permeability cap at the ground surface for keeping high temperatures away from the surface. The most effective design appears to be a combination of a low-permeability surface cap and air injection above the steam injector. The cap mainly serves to direct the air flow, preventing it from exiting at the ground surface near the air injection point.

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