ABSTRACT
Passive soil vapor extraction (PSVE) relies on the naturally occurring variations in barometric pressure (Ellerd et al. 1999, Rossabi 1998). In Denmark, these oscillations are primarily resulting from passage of weather fronts. As the barometric pressure rises, a gradient is imposed on the soil gas, which drives fresh air into the soil. When the barometric pressure drops, soil gas will ascend into the atmosphere. When low permeability layers are present, they tend to damp and delay the pressure signal in the deeper vadose zone, resulting in a net varying vertical gradient. Boreholes screened in this vadose zone will act as a preferred flow path, and a significant flow of VOC contaminated soil gas out of the borehole will be the result of the pressure gradient. Different ways to enhance and control the flow out of boreholes have been investigated. These include one-way valves allowing outflow only, GAC-canisters to adsorb the VOCs and different depths to the screened portion of the boreholes.
