Passive Soil Vapor Extraction - GSI Environmental Inc.

SRNL-STI-2009-00571Rev. 11.3 How It WorksBarometric Applications: Disequilibrium between the atmospheric pressure and thesubsurface pressure results in a flow of air from the zone of high pressure to the zone oflow pressure when the two zones are directly connected as by a well. As a result of thispressure difference, under natural circumstances, wells screened within the unsaturatedzone have been shown to “breathe”, i.e., inhale ambient air from the atmosphere duringhigh atmospheric pressure conditions and exhale soil gas to the atmosphere during lowatmospheric pressure conditions. Barometric applications aim to exploit the “exhalation”behavior in wells screened within the impacted soil layers in the unsaturated zone byinstalling a passive one-way check valve that allows flow of soil gas into the atmospherewhen the pressure in the well is greater than the atmospheric pressure and seals thewell when the atmospheric pressure is greater than the pressure in the well. Bypreventing dilution of soil gas with ambient air, the one-way passive control valve hasbeen shown to increase mass removal of VOCs by barometric pumping by at least afactor of 2 (Rohay et al. 1997; Rossabi, 1999). A network of such wells screened withincontaminated layers of the vadose zone could effectively remove residual contaminantmass during the course of a long-term remediation project.In the last 10 years, researchers have explored a variety of check valves for use inbarometric applications:1. Mylar Flapper Valve patented by Science and Engineering Associates and used inconjunction with Barometrically Enhanced Remediation Technology (BERT TM )(ITSER, 2000);2. Mylar Disk patented by Idaho National Engineering and Environmental Laboratory(INEEL); and3. Baroball TM Control Valve is a trademark of Westinghouse Savannah River Company,LLC.Figure 1.1: Devices used for Barometric Applications: (a) BERT TM Flapper Valve; (b)Baroball TM Control Valve2 Enhanced Attenuation TechnologiesPassive Soil Vapor Extraction