Barometric pumping with a twist: VOC containment and remediation without boreholes

A large national cost is incurred in remediating near-surface contamination such as surface spills, leaking buried pipelines, and underground storage tank sites. Many of these sites can be contained and remediated using enhanced natural venting, capitalizing on barometric pumping. Barometric pumping is the cyclic movement experienced by soil gas due to oscillations in atmospheric pressure. Daily variations of 5 millibars are typical, while changes of 25 to 50 millibars can occur due to major weather front passage. The fluctuations can cause bulk vertical movement in soil gas ranging from centimeters to meters, depending on the amplitude of the pressure oscillation, soil gas permeability, and depth to an impermeable boundary such as the water table. Since the bulk gas movement is cyclic, under natural conditions no net advective vertical movement occurs over time. Science and Engineering Associates, Inc., is developing an engineered system to capitalize on the oscillatory flow for soil contaminant remediation and containment. By design, the system allows normal upward movement of soil gas but restricts the downward movement during barometric highs. The earth`s surface is modified with a sealant and vent valve such that the soil gas flow is literally {open_quotes}ratcheted{close_quotes} to cause a net upward flow over time. A key feature of the design is that it does not require boreholes, resulting in a very low cost remediation effort and reduced personnel exposure risk. In the current phase (Phase I) the system`s performance is being evaluated. Static and transient analysis results are presented which illustrate the relative magnitude of this advective movement compared to downward contaminant diffusion rates. Calculations also indicate the depth of influence for various surface and soil configurations. The system design will be presented, as well as a cost assessment compared to conventional techniques