Page 205 - Materials Chemistry, Second Edition

188 Practical Design Calculations for Groundwater and Soil Remediation

As shown in Example 2.38, the values of S (the adsorbed COC concentra-
tion on the soil surface) and X (the COC concentration of the soil sample) are
relatively similar for compounds like benzene; while the ratio of the X and S
values is essentially the ratio of the dry bulk density and total bulk density
for very hydrophobic compounds such as pyrene. For either case, the follow-
ing relationship is valid:

S final X final
≈ (5.28)
S initial X initial

By inserting Equation (5.28) into Equations (5.25), (5.26), and (5.27), we
can obtain:

1
≈ =
X final S final
V l
X initial S initial 1+ ( M s,dry ) (5.29)
K p
1
X final ≈ × X initial
1+ ( M s,dry ) (5.30)
V l
K p
1 1 1
X final S final
≈ = × × × .
V l,2
V l,1
V l,3
X initial S initial 1+ ( M s,dry ) 1+ ( M s,dry ) 1+ ( M s,dry ) (5.31)
K p K p K p
The relationship among mass of soil before washing (M s,wet ), mass of dry
soil (M s,dry ), dry bulk density (ρ ), and total bulk density (ρ ) can be found
b
t
from the following linear relationship:
M s,dry b ρ
≈ (5.32)
M s,wet t ρ
Example 5.20: Determine the Efficiency of Soil Washing
A sandy subsurface contains 500 mg/L of 1,2-dichloroethane (DCA) and 500
mg/L of pyrene. Soil washing is proposed to remediate the soil. A batch
washer that can accommodate 1,000 kg of soil is designed. For each batch of
operation, 1,000 gal of clean water is used as the washing fluid. Determine
the final concentrations of these two COCs in the washed soil.
Use the following data from site assessment in design:
• Dry bulk density of soil = 1.6 g/cm 3
• Total bulk density of soil = 1.8 g/cm 3
• Fraction of organic carbon of aquifer materials = 0.005
• K = 0.63 K ow
oc