This phenomenon is called co-distillation or co-boiling. Table 3.4 shows this
phenomenon for selected NAPL compounds.
3.2.2.2 Influence of Temperature on the Henry’s Law Constant
The Henry’s law constant is the ratio of a compound’s partial pressure in the gas
phase (atm) to the concentration of the compound in aqueous phase (molÁm
À3 ) at a
given temperature. The dimensionless Henry’s law constant is temperature dependent. It may be corrected for the average soil temperature using the Clausius–
Clapeyron relationship (Eq. 3.7) (Perry et al. 1997; USEPA 2001):
k
0
H TS
ð Þ ¼
exp À
Δ H
R
1 À 1
À
Á
h
i
k H R
ð Þ
RT s
ð3:7Þ
where,
k
0
H(TS) : dimensionless Henry’s law constant at the average soil temperature (À)
ΔH v,TS : enthalpy of vaporization at the average soil temperature (calÁmol
À1 )
T S : average soil temperature (K)
Fig. 3.6 Vapor pressure of various contaminants as a function of temperature (Stegemeier and
Vinegar 2001)
160
S. Colombano et al.