Page 193 - Materials Chemistry, Second Edition

176 Practical Design Calculations for Groundwater and Soil Remediation

for each interval. The total cleanup time can then be derived from summing
the cleanup time of each interval. The following steps detail this approach:

Step 1: Determine the maximum possible COC concentration in soil in the
absence of free product, X (see Example 5.3). If the average con-
sat
centration of the soil samples exceeds this value, the free-product
phase is present. Go to Step 2. If the average concentration of the
samples is smaller, the free-product phase is absent. Go to Step 5.
Step 2: Estimate the extracted vapor concentration using Equation (5.1)
and then calculate the mass removal rate using Equation (5.9).
Step 3: Determine the amount of COCs to be removed before the disap-
pearance of the free-product phase by using modified Equation
(5.11) as

M removal = (X initial – X )(M ) = (X initial – X )[(V)(ρ )] (5.12)
sat
s
t
sat
s
Step 4: Determine the required time for removal of the free product by
using data from Steps 2 and 3 and Equation (5.10).
Step 5: Divide the (X − X cleanup ) value into a few intervals. Use the
sat
average X of each interval to estimate the vapor concentration
(see Example 5.5), and then calculate the mass removal rate
using Equation (5.9). If no free-product phase is present initially,
replace X with X initial in this step.
sat
Step 6: Determine the amount of COCs to be removed in each interval
by using modified Equation (5.11):

M removal = (X initial − X final )(M ) = (X initial − X final )[(V)(ρ )] (5.13)
t
s
s
Step 7: Determine the required cleanup time for each interval by using
data from Steps 5 and 6 and Equation (5.10).
Step 8: Sum the required time for each interval to calculate the total
cleanup time.

Information needed for this calculation:
• COC concentrations of soil samples
• Henry’s constant of the COC
• Organic–water partition coefficient, K ow
• Organic content, f oc
• Porosity, ϕ
• Degree of water saturation