Page 73 - Materials Chemistry, Second Edition

56 Practical Design Calculations for Groundwater and Soil Remediation

an organic content of 2%. The subsurface temperature is 20°C. Estimate the
maximum concentrations of TCA in the soil moisture and on the soil grains.

Solution:
(a) With a concentration of 1,320 ppmV, this is 100 times smaller
than that in Example 2.32:
G = 1,320 ppmV = 7,320 mg/m = 7.32 mg/L
3
(b) With dimensionless Henry’s constant of 0.60 (from Example
2.32):
G = HC = 7.32 mg/L = (0.60)C
So, C = 12.2 mg/L = 12.2 ppm
(c) With K = 3.82 L/kg,
p
S = K C = (3.82 L/kg)(12.2 mg/L) = 46.6 mg/kg
p
Discussion:
1. The equilibrium relationships (G = HC and S = K C) are linear.
p
With a vapor concentration of 1,320 ppmV, which is 100 times
smaller than that (132,000 ppmV) in Example 2.32, the corre-
sponding liquid and solid concentrations are correspondingly
smaller by 100 times. It should be noted that this is only valid
when two systems have the same characteristics (i.e., same H and
K values).
p
2. The concentrations are based on an assumption that the system
is in equilibrium; the actual values would be different if the sys-
tem is not in equilibrium.

2.4.5 Partition of COCs in Different Phases

The total mass of COCs in the vadose zone is the sum of the mass in four
phases (vapor, moisture, solid, and free product). Let us consider a COC
plume in the vadose zone with a volume, V.
From Equation (2.5),

mass of COC dissolved in the soil moisture = (V)(C) = [V(ϕ )]C (2.29)
l
w
From Equation (2.6),

mass of COC adsorbed onto the soil grains = (M )(S) = [V(ρ )]S (2.30)
b
s
From Equation (2.7),

mass of COC in the void space = (V )(G) = [(V)(ϕ )]G (2.31)
a
a