TABLE 4-2 Summary of Thermal Technology Applications by Technology Type (1988-2007)

Technology Number of Applications Pilot-Scalea Full-Scalea Number Since Year 2000
Steam-Based 46 26 19 15
Electrical Resistance Heating 87 23 56 48
Conduction 26 12 14 17
Other/Radio-Frequency 23 14 9 4
Total 182 75 98 84

aSome sites have an unknown application size and thus are not included in the pilot- and full-scale count.

SOURCE: Reprinted, with permission, from Triplett Kingston (2008).

Meldau, 1979; Vinegar et al., 1999). All involve raising the temperature of the subsurface to enhance the removal of contaminants by separate-phase liquid extraction, mobilization, volatilization, and in situ destruction. Relative to other technologies, some in situ thermal treatment technologies (e.g., ERH) applications result in preferential heating and contaminant removal from lower permeability media.

A review of the application of these technologies was conducted by Triplett Kingston (2008) and Triplett Kingston et al. (2009, 2010a,b, 2012). Data and documents from 182 thermal treatment applications conducted between 1988 and 2007 were reviewed, including 87 ERH, 46 steam-based heating, and 26 conductive heating applications. The applications were categorized based on the hydrogeology of the site, using the five generalized hydrogeologic scenarios developed in NRC (2005). These include relatively homogeneous and permeable unconsolidated sediments (Scenario A), largely impermeable sediments with inter-bedded layers of higher permeability material (Scenario B), largely permeable sediments with inter-bedded lenses of low-permeability material (Scenario C), competent, but fractured bedrock (Scenario D), and weathered bedrock, limestone, sandstone (Scenario E). The majority (72 percent) of thermal remediation applications reviewed were conducted in settings containing layers of high- and low-permeability media (Scenarios B and C).

ERH applications accounted for about 50 percent of all thermal applications since 2000 and outnumbered each of the other technology applications by about a factor of 3; there also appeared to be increasing use of conductive heating and decreasing use of steam-based heating (Table 4-2). These trends are reflective of underlying technical factors controlling performance, as well as design and operating challenges and vendor avail-

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