Subsurface temperature is an important environmental
variable in SVE remediation processes. The efficiency of SVE
remediation is strongly linked to the vapor pressures of the
target compounds with a suggested lower limit on vapor pressure
of 
1000 Pa [ Peterson et al. , 1988;
Johnson et al. , 1990a]. Vapor pressures of
organic compounds increase by a factor of approximately 3 or
4 with every 10
C rise in temperature. Experimental
evidence also suggests that vapor sorption is inversely
proportional to temperature [ Goss, 1992].
The effect of subsurface temperature on the design and operation
of BV remediation efforts has received little attention. It is
generally accepted that soil temperatures at most sites are
within the limits for microbial growth [
Litchfield, 1993]. In Alaska, where soil temperatures are as
low as 1
C, respiration rates comparable to those in
temperate and subtropical regions were observed
during summer months [ Ong et al. , 1994;
Kellems et al. , 1994]. The observed rates dropped
slightly during the winter months with less effect noted at
sites with either active or passive soil warming.
Methods to increase SVE efficiency by increasing the
subsurface temperature have been attempted. At a
diesel contaminated site, ambient air was heated to 177
C
before injection [ Sittler et al. , 1993].
Increases in subsurface air temperatures of up to 28
C
were observed as far as 9m from the nearest injection well.
Steam injection for removal of NAPLs in the saturated zone has
also been studied [ Hunt et al. , 1988;
Falta et al. , 1992; Wilson and
Clarke, 1992; Adenekan and Patzek, 1993].
Other novel approaches integrating SVE with methods for soil
heating are described by Downey and Elliott [1990].