Handbook of Solvents - George Wypych - ChemTech - Ventech!

1578 Hanadi S. Rifai, Charles J. Newell, Todd H. Wiedemeier
23.1.2.6 Volatilization
Volatilization causes contaminants to transfer from the dissolved phase to the gaseous
phase. In general, factors affecting the volatilization of contaminants from ground water
into soil gas include the contaminant concentration, the change in contaminant concentration
with depth, the Henry’s Law constant and diffusion coefficient of the compound, mass
transport coefficients for the contaminant in both water and soil gas, sorption, and the temperature
of the water. 21
The Henry’s Law constant of a chemical determines the tendency of a contaminant to
volatilize from ground water into the soil gas. Henry’s Law states that the concentration of a
contaminant in the gaseous phase is directly proportional to the compound’s concentration
in the liquid phase and is a constant characteristic of the compound: 11
Ca = HCl
[23.1.12]
where:
H Henry’s Law constant (atm m 3 /mol)
Ca concentration in air (atm)
Cl concentration in water (mol/m 3 )
Values of Henry’s Law constants for selected chlorinated solvents are given in Table
23.1.2. As indicated in the table, values of H for chlorinated compounds also vary over several
orders of magnitude. Chlorinated solvents have low Henry’s Law constants, with the
exception of vinyl chloride. Volatilization of chlorinated solvents compounds from ground
water is a relatively slow process that generally can be neglected when modeling
biodegradation.
Table 23.1.2. Physical properties for chlorinated compounds
Constituent
CAS
#
Molecular
weight
M W,
g/mol Ref
D air,
cm 2 /s
Diffusion coefficients
in air in water
Ref
D wat,
cm 2 /s
Ref
log Koc
(@20-25°C)
Partition
log(L/kg)
Bromodichloromethane 75-27-4 163.8 22 2.98E-02 22 1.06E-05 22 1.85 22
Carbon tetrachloride 56-23-5 153.8 22 7.80E-02 22 8.80E-06 22 2.67 22
Chlorobenzene 108-90-7 112.6 22 7.30E-02 22 8.70E-06 22 2.46 22
Chloroethane 75-00-3 64.52 22 1.50E-01 22 1.18E-05 22 1.25 22
Chloroform 67-66-3 119.4 22 1.04E-01 22 1.00E-05 22 1.93 22
Chloromethane 74-87-3 51 23 1.28E-01 22 1.68E-04 b 1.40 28
Chlorophenol, 2- 95-57-8 128.6 22 5.01E-02 22 9.46E-06 22 2.11 22
Dibromochloromethane 124-48-1 208.29 22 1.99E-02 22 1.03E-05 22 2.05 22
Dichlorobenzene, (1,2)(-o) 95-50-1 147 22 6.90E-02 22 7.90E-06 22 3.32 22
Dichlorobenzene, (1,4)(-p) 106-46-7 147 22 6.90E-02 22 7.90E-06 22 3.33 22
Dichlorodifluoromethane 75-71-8 120.92 22 5.20E-02 22 1.05E-05 22 2.12 22
Ref