Page 175 - Materials Chemistry, Second Edition

158 Practical Design Calculations for Groundwater and Soil Remediation

Example 5.3: Determine if the Free-Product Phase Is Present in
Subsurface Using the Saturated Vapor Concentration
A subsurface is impacted by a spill of 1,1-dichloroethane (1,1-DCA). The 1,1-
DCA concentrations of the soil samples from the impacted zone were between
6,000 to 9,000 mg/kg. The subsurface has the following characteristics:

• Porosity = 0.4
• Organic content in soil = 0.02
• Degree of water saturation = 30%
• Subsurface temperature = 20°C
• Dry bulk density of soil = 1.6 g/cm 3
• Total bulk density of soil = 1.8 g/cm 3

Determine if the free-product phase of 1,1-DCA is present in the subsurface.
What could be the maximum 1,1-DCA concentration in soil if the free-prod-
uct phase of 1,1-DCA is absent?

Solution:
(a) From Table 2.5, the following physicochemical properties of 1,1-
DCA were obtained:

Molecular weight = 99.0
H = 4.26 atm/M
P vap = 180 mm-Hg
log K = 1.80
ow
(b) Use Equation (5.1) to determine the saturated 1,1-DCA vapor
concentration:

P vap = 180 mm-Hg = 0.237 atm = 237,000 ppmV

(c) Convert the saturated vapor concentration into a mass concen-
tration by using Equation (2.1):

1 ppmV of 1,1-DCA = (99.0)/24.05 = 4.12 mg/m 3
So, G = 237,000 ppmV = (237,000)(4.12)
sat
= 976,000 mg/m = 976 mg/L
3
(d) Use Table 2.4 to convert the Henry’s constant to a dimensionless
value:

H = H/RT = (4.26)/[(0.082)(273+20)] = 0.177 (dimensionless)
*