Environmental Engineering Reference
In-Depth Information
TABLE 3.2
Calculated Relative Mass Flux Estimates (Chemical Volatilization Rates) of Chlorinated
Solvents and Stabilizer Compounds from Dry Soil for a 10 L Spill in a 1.5 m
2
Area
Molecular
Weight
(g/mol)
Mass
Fraction in
Soil
b
(%)
Diffusion
Constant
c
D
a
Mass
Flux
d
Q
(g/s)
Vapor Pressure
(mm Hg, 25°C)
Density
(g/cm
3
)
10 L Spill
Mass (g)
Compound
a
Dichloromethane
84.93
355
1.3255
13,255
0.79
0.101
22.0
1,2-Butylene oxide
72.11
207
0.8297
8297
0.50
0.135
9.1
Methyl chloroform
133.42
100
1.3376
13,376
0.80
0.078
7.6
Trichloroethylene
131.39
60
1.4642
14,642
0.88
0.079
5.0
1,3-Dioxolane
74.08
70
1.06
10,600
0.63
0.146
4.4
1,4-Dioxane
88.1
38.09
1.0329
10,329
0.62
0.229
4.3
Cyclohexane
84.18
96.9
0.779
7790
0.47
0.089
3.1
Nitromethane
61
35.8
1.1322
11,322
0.68
0.116
1.6
tert
-Butyl alcohol
74.12
40.7
0.78581
7858
0.47
0.115
1.5
Perchloroethylene
165.83
14
1.6227
16,227
0.97
0.072
1.5
Nitroethane
75.08
20.8
1.0448
10,448
0.63
0.165
1.5
Epichlorohydrin
92.52
16.4
1.175
11,750
0.70
0.086
0.8
sec
-Butyl alcohol
74.12
18.3
0.8063
8063
0.48
0.101
0.6
tert
-Amyl alcohol
88.15
13.8
0.8096
8096
0.48
0.102
0.5
Triethanolamine
149.19
1.1242
11,242
0.67
0.121
3.59 × 10
−06
4 × 10
−07
a
Nonitalics compounds are stabilizers. Italics compounds are chlorinated solvents; these are listed for comparison to show
whether the stabilizer is likely to evaporate with the solvent or remain behind in the soil where it can be leached down to
groundwater.
b
Mass fraction = grams of compound per gram of soil, if soil bulk density is assumed to be 1.85 g/cm
3
.
c
Air diffusion constants shown in italic font were estimated by using Equation 3.1, with temperature set to 25°C.
d
Mass l ux was calculated by using the Shen (1981) equation (Equation 3.4 in the text).
from soil are found in Dragun (1988). Calculated estimates of the relative mass l ux of chlorinated
solvents and stabilizer compounds from dry soil to air are provided in Table 3.2.
The Shen estimate of relative volatilization rates from dry soil isolates one mode of transfer, but
discharge of a single chemical to dry soil is an uncommon occurrence. Generally, wastes are
discharged as complex mixtures of chlorinated solvents with concentrated stabilizers, oil, grease,
soldering l ux, acids, and water. Soil-water plays an important role in the fate and transport of
chemicals discharged to soil. Mixtures of wastes will partition from moist soil to air according to
their solubilities, vapor pressures, chemical stability, and capacity to adsorb to soil minerals and
organic matter. As discussed in the next section, the interaction of the chemical at the water-air
interface plays an important role in fate and transport processes.
3.1.3 V
OLATILIZATION
FROM
W
ATER
Several possible fate and transport mechanisms act on a chemical discharged to wet soil, groundwa-
ter, or surface water. The propensity for a chemical to partition between aqueous and vapor phases
is a well-studied phenomenon, as Henry's law mathematically describes.
3.1.3.1 Henry's Law
The constant describing the equilibrium concentration of a compound in both the aqueous and
vapor phases at the liquid-air interface at a i xed temperature is called the Henry's law constant.
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