Barometric pumping

The hydrocarbon flux near to the surface varies according to the supply of hydrocarbons and whether local chemical and biological conditions favour their preservation or breakdown. In addition, hydrocarbon magnitudes at any given location vary with time because of displacement by wind, rain and barometric pumping (Wyatt et al., 1995). 

In a very extensive review. Price (1985) suggested that surface bacterial activity can totally obliterate the gases in a microseep. That this is not typically the case has been demonstrated by extensive research over both macroseeps and microseeps (Jones, 1984). However, bacterial activity does probably contribute to the noisy appearance of soil-gas seepage. 

Thus the main difficulty with atmospheric sampling is created by meteorological changes which can greatly displace and dilute the seepage emissions. In addition, it is clear that the stress fields in the Earth can also influence this gas flux significantly. 

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The Barometrically Enhanced Remediation Technology (BERT ) removes and recovers volatile organic contaminants from soil by enhancing the natural air exchange that occurs in soil as a response to changes in atmospheric pressure. This process is sometimes referred to as barometric pumping or passive soil vapor extraction. The process is a low-cost complement to conventional active-extraction methods because investment and maintenance costs are low and no power is needed. The passive process is better suited than conventional methods for certain problems. 

Key words unsaturated zone barometric pumping natural remediation... 

The indirect effects of barometric pumping are derived from an analysis of the one-dimensional air-phase transport equation ... 

Dispersion arises from the fact that, even in a relatively homogenous porous medium, small-scale heterogeneities exist which cause airflow to proceed along various channels at different rates. Barometric pumping causes a significant increase in the coefficient of hydrodynamic dispersion over a pure diffusion-based transport model, thus increasing the overall transport rate. 

In a recent study, Elberling et al. (1998) looked at the effect of barometric pumping on the transport of atmospheric oxygen within the... 

Failing to incorporate soil-gas advection induced by barometric pumping into gas-phase subsurface transport models may, under certain conditions, under predict contaminant flux to the atmosphere. As previously described, Smith et al. (1996) compared TCE vapor fluxes measured with a chamber device to TCE in groundwater being removed by a pump-and-treat system and discharge into a surface-water receiving body at the same site. These researchers found VOC removal rates by flux to the atmosphere comparable in magnitude to both of the other attenuation pathways. 

Finally, Chapters 14 and 15 address the remediation of the unsaturated zone. In Chapter 14, researchers from the University of Virginia study the effects of natural atmospheric pressure variations on the flow of air into and out of the unsaturated zone at the Picatinny Arsenal in northern New Jersey. This barometric pumping contributes to the natural remediation of the shallow, trichloroethylene-contaminated groundwater. In the last chapter of the book, Richard Meixner and co-workers present a detailed field study documenting the effectiveness of soil-vapor extraction to remediate gasoline hydrocarbons in the unsaturated zone. 

Contaminants in the soil compartment are associated with the soil, water, air, and biota phases present. Transport of the contaminant, therefore, can occur within the water and air phases by advection, diffusion, or dispersion, as previously described. In addition to these processes, chemicals dissolved in soil water are transported by wicking and percolation in the unsaturated zone.26 Chemicals can be transported in soil air by a process known as barometric pumping that is caused by sporadic changes in atmospheric pressure and soil-water displacement. Relevant physical properties of the soil matrix that are useful in modeling transport of a chemical include its hydraulic conductivity and tortuosity. The dif-fusivities of the chemicals in air and water are also used for this purpose. 

BRn3, = the cumulative yield branching ratio for thermal fission of leading to Xe = 0.067 = barometric pumping factor ratio = 1. 

Aeration of the soil due to absolute pressure changes also leads to mass flow of gases in soil. Continuous meteorological pressure variations in the atmospheric air above the soil are the principal driving force. This barometric pumping causes atmospheric air to... 

Wyatt, D.E., Richers, D.M. and Pirkle, R.J., 1995. Barometric pumping effects on soil gas studies for geologic and environmental characterization. Environmental Geol., 25 243-250. 

Auer, L. H., N. D. Rosenberg, K. H. BirdseU, and E. M. Whiteny. 1996. The effects of barometric pumping on contaminant transport. Journal of Contaminant Hydrology 24 ... 

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