Page 174 - Materials Chemistry, Second Edition

Vadose Zone Soil Remediation 157

moisture, and the saturation of soil pore gas have been achieved. Above this
saturation concentration, free product must be present. Equation (2.40) can
be modified by replacing C with COC solubility in water (S ) and G with
w
vapor concentration in equilibrium with free product (G ) as
sat
 [( w + ρ K p + φ H 
φ
( )]
)( )
X sat =  b a  × S w
 t ρ 
  ( w ) + ( b ) K p + ()   (5.2)
ρ
φ
a φ

 ×
=   H H   G sat
 t ρ 
 
To determine if the free-product phase is present, the following procedure
can be used:
Step 1: Obtain the physicochemical data of the COC (e.g., from Table 2.5).
Step 2: Assume the free-product phase is present. Use Equation (5.1) to
determine the saturated vapor concentration.
Step 3: Convert the saturated vapor concentration into a mass concen-
tration by using Equation (2.1).
Step 4: Determine the K value using Equation (2.28) and K value
p
oc
using Equation (2.26).
Step 5: Determine the COC concentration in soil by using Equation (5.2)
and the vapor concentration from Step 3 (or by using Equation
(5.2) and the solubility in water).
Step 6: If the soil saturation concentration in soil determined from Step
5 is smaller than the concentrations of the soil samples, the free-
product phase should be present.

Information needed for this calculation:

• Vapor pressure of the COC (or the solubility in water)
• Molecular weight of the COC
• Henry’s constant of the COC
• Organic–water partition coefficient, K ow
• Organic content, f oc
• Porosity, ϕ
• Degree of water saturation
• Dry bulk density of soil, ρ b
• Total bulk density of soil, ρ t