Page 80 - Materials Chemistry, Second Edition

Site Assessment and Remedial Investigation 63

(e) Determine the mass fraction in each phase

Benzene Pyrene
% in void 2.8 4.9 × 10 −6
% in moisture 5.4 0.01
% in solid 91.8 99.99

Discussion:
For both compounds, most of the COCs are attached onto the solid
(91.8% for benzene and 99.99% for pyrene). This is especially true for
pyrene that has very high K and low H values. The vapor concen-
p
tration of pyrene is extremely low, while its concentration in soil is
very high.

Example 2.38: COC Concentrations in Soil: A Comparison of S and X
In Example 2.37, the concentrations of benzene and pyrene adsorbed onto
the soil grains were found to be 1.89 and 301 mg/kg, respectively. If a sample
was taken from that location and analyzed for benzene and pyrene concen-
tration in soil by a laboratory, what would be the concentration values of the
soil samples? Use these values to estimate the total COC mass in soil.

Solution:
(a) The values of X and S are related by Equation (2.40)
  φ ( w ) +ρ +φ () H  
 × S
X =    K p b a K P  
 ρ t 
 
X = {[(0.12)/(1.28) + 1.6 + (0.28)(0.22)/(1.28)] ÷ 1.8} × 1.89
= 1.83 mg/kg (for benzene)
X = {[(0.12)/(717) + 1.6 + (0.28)(0.0002)/(717)] ÷ 1.8} × 301
= 268 mg/kg (for pyrene)
(b) If the COC mass in the void was not captured in the laboratory
analysis, Equation (2.40) can be modified to:
  φ ( w ) +ρ  
X =    K p b    × S
 ρ t 
 

X = {[(0.12)/(1.28) + 1.6] ÷ 1.8} × 1.89
= 1.78 mg/kg (for benzene)
X = {[(0.12)/(717) + 1.6] ÷ 1.8} × 301
= 268 mg/kg (for pyrene)