Environmental Modeling - Mathematics and Statistics for the Environment - page 88

TABLE 3.1
Henry's Law Constants ( H )

Henry's Law Constant
(atm × m 3 /mol)

Chemical (dimensionless)

Aroclor 1254

2.7 × 10 -3 1.2 × 10 -1

Aroclor 1260

7.1 × 10 -3 3.0 × 10 -1

Atrazine

3 × 10 -9 1 × 10 -7

Benzene

5.5 × 10 -3 2.4 × 10 -1

Benz[ a ]anthracene

5.75 × 10 -6 2.4 × 10 -4

Carbon tetrachloride

2.3 × 10 -2 9.7 × 10 -1

Chlorobenzene

3.7 × 10 -3 1.65 × 10 -1

Chloroform

4.8 × 10 -3 2.0 × 10 -1

Cyclohexane 0.18 7.3

1,1-Dichloroethane 6 × 10 -3 2.4 × 10 -1

1,2-Dichloroethane 10 -3 4.1 × 10 -2

cis -1,2-Dichloroethene 3.4 × 10 -3 0.25

trans -1,2-Dichlorethene 6.7 × 10 -3 0.23

Ethane 4.9 × 10 -1 20

Ethanol 6.3 × 10 -6

—

Ethylbenzene 8.7 × 10 -3 3.7 × 10 -1

Lindane 4.8 × 10 -7 2.2 × 10 -5

Methane 0.66 27

Methylene chloride

3 × 10 -3 1.3 × 10 -1

n -Octane 2.95 121

Pentachlorophenol 3.4 × 10 -6 1.5 × 10 -4

n -Pentane 1.23 50.3

Perchloroethane

8.3 × 10 -3 3.4 × 10 -1

Phenanthrene

3.5 × 10 -5 1.5 × 10 -3

Toluene

6.6 × 10 -3 2.8 × 10 -1

1,1,1-Trichloroethane (TCA)

1.8 × 10 -2 7.7 × 10 -1

Trichloroethene (TCE)

1 × 10 -2 4.2 × 10 -1

o -Xylene

5.1 × 10 -3 2.2 × 10 -1

Vinyl chloride 2.4 99

Source: Adapted from Lyman, W.J. et al., Handbook of Chemical
Property Estimation Methods , American Chemical Society,
Washington, DC, 1990.

the primary transport mechanisms at the macroscopic level. Transport by molecular diffusion and
mixing is referred to as dispersive transport ; transport by bulk movement of the medium is referred
to as advective transport . Advective and dispersive transports are fluid-element driven. Advection,
for example, is the movement of dissolved solute with flowing groundwater. The amount of con-
taminant being transported is a function of its concentration in the groundwater and the quantity of
groundwater flowing, and advection will transport contaminants at different rates in each stratum.
Diffusive transport, on the other hand, is the process by which a contaminant in water will move
from an area of greater concentration toward an area where it is less concentrated. Diffusion will
occur as long as a concentration gradient exists, even if the fluid is not moving, and as a result a
contaminant may spread away from the place where it is introduced into a porous medium.