Soil vapor extraction

In the vadose (unsaturated) zone, liquid organic compounds partition into four distinct but related phases NAPL adsorbed onto soil particles, free-phase NAPL, soluble constituents in soil water, and vapor-phase components as part of the soil 

Sites suitable for conventional SVE have certain typical characteristics. The contaminating chemicals are volatile or semivolatile (vapor pressure of 0.5 mm Hg or greater). Removal of metals, most pesticides, and PCBs by vacuum is not possible because their vapor pressures are too low. The chemicals must be slightly soluble in water, or the soil moisture content must be relatively low. Soluble chemicals such as acetone or alcohols are not readily strippable because their vapor pressure in moist soils is too low. Chemicals to be removed must be sorbed on the soils above the water table or floating on it (LNAPL). Volatile dense nonaqueous liquids (DNAPLs) trapped between the soil grains can also be readily removed. The soil must also have sufficiendy high effective porosity (permeability) to allow free flow of air through the impacted zone. 

High concentrations of low-solubility compounds with higher vapor pressures will result in greater quantities that will be removed with each flush volume of air. The vacuum developed by the pump, the airflow rate, and the temperature are other factors that also affect removal rates. 

Where the volatile compounds are present in soil with low permeability, use of high-vacuum (i.e., up to 25 in Hg) extraction has been successful. Such low pressures enhance evaporation of both contaminants and water attached to the soil particles. 

FIGURE 10.4 Relationship between soil water content and relative air permeability. 

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A U.S. EPA study (41) showed that soil vapor extraction (SVE) is an effective treatment for removing volatile contaminants from the vadose zone. Sandy soils are more effectively treated than clay or soils with higher organic content because higher air flows are possible in sand and clays—organic soils tend to adsorb or retain more contaminants. Removal of volatiles is rapid in the initial phase of treatment and thereafter decreases rapidly thereafter-an important consideration in the design of air emissions control over the life of the project. 

Economic feasibility studies suggest that even at the present state of the art photocatalytic technology indeed can be competitive with the traditional carbon adsorption or incineration technologies in treatment of contaminated soil vapor extraction vents and small scale VOC-containing vents [28]. Rapid progress in basic and applied research in photocatalysis suggests... 

Soil vapor extraction (SVE) is a relatively new yet widely applied technology for the remediation of soils contaminated with volatile organic compounds (VOC) in the unsaturated zone above the water table (vadose zone). The process consists of generating an airstream through the contaminated soil subsurface in order to enhance the volatilization of organic contaminants and thus remove them from the soil matrix.913... 

Soil vapor extraction has become a very popular technology since the mid-1990s, because it has several important advantages ... 

Kirtland, B.C. and Aelion, C.M., Petroleum mass removal from low permeability sediment using air sparging/soil vapor extraction impact of continuous or pulsed operation, J. Contam. Hydrol., 41, 367-383, 2000. 

Poppendieck, D.G., Loehr, R.C. and Webster, M.T., Predicting hydrocarbon removal from thermally enhanced soil vapor extraction systems. 2. Field study, J. Hazard. Mater., 69, 95-109, 1999. 

Lowe, D.F., Oubre, C.L. and Ward, C.H., Eds., Soil vapor extraction using radio frequency heating, in Resource Manual and Technology Demonstration, Lewis Publishers, Boca Raton, FL, 1999. 

Falta, R.W., Pruess, K. and Chestnut, D.A., Modeling advective contaminant transport during soil vapor extraction, Ground Water, 31, 1011-1020, 1993. 

Campagnolo, J.F. and Akgerman, A., Modeling of soil vapor extraction (SVE) systems—Part I, Waste Management, 15, 379-389, 1995. 

Rathfelder, K.M., Lang, J.R. and Abriola, L.M., A numerical model (MISER) for the simulation of coupled physical, chemical and biological processes in soil vapor extraction and bioventing systems, J. Contam. Hydrol., 43, 239-270, 2000. 

Soil vapor extraction (SVE) can be used to remove volatile contaminants and, when combined with another technology, to treat nonvolatile contaminants. If contamination has reached the aquifer, it is necessary to use SVE in combination with groundwater pumping and air stripping. 

FIGURE 16.17 Soil vapor extraction and air sparging. (Taken from Rohayo, A.J., Cameron, R.J., Teters, B.B., Rossabi, J., Riha, R., and Downs, W., Passive Soil Vapor Extraction, Technical Report DE98051208, 20 p., U.S. Department of Commerce, National Technical Information Service, Springfield, VA, 1997. With permission.)... 

Alternative 3 (In Situ Soil Vapor Extraction, Cap, Groundwater Pump-and-Treat)... 

Removal of Gasoline from Contaminated Soil 18.8.4.1 In Situ Soil Vapor Extraction... 

TESVE Thermal-enhanced soil vapor extraction... 

U.S. EPA, Engineering Bulletin In Situ Soil Vapor Extraction Treatment, EPA/540/2-91/006, Hazardous Waste Engineering Laboratory, U.S. EPA, Washington, 1991. 

Sittler, S.P. and Swinford, G.L., Thermal-enhanced soil vapor extraction accelerates cleanup of diesel-affected soils, Natl. Environ. J., January, 40-43, 1993. 

Symons, B.D. and Greene, J., Soil vapor extraction, bioventing, and air sparging, in MTBE Remediation Handbook, Moyer, E.E. and Kostecki, P.T., Eds, Amherst Scientific Publishers, Amherst, MA, 2003. 

U.S. EPA, Eight Service Stations in Maryland Soil Vapor Extraction and Groundwater Extraction Used to Treat Soil and Groundwater, MTBE Case Study, United States Environmental Protection Agency, Washington, DC, July 2000. 

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