Page 69 - Materials Chemistry, Second Edition

52 Practical Design Calculations for Groundwater and Soil Remediation

The organic carbon partition coefficient (K ) can be considered as the
oc
partition coefficient for the organic compound into a hypothetical pure
organic carbon phase. For soil that is not 100% organics, the partition coef-
ficient is discounted by the factor, f . Clayey soil is often associated with
oc
more natural organic matter and, thus, has a stronger adsorption potential
for organic COCs.
K is actually a theoretical parameter, and it is the slope of experimentally
oc
determined K vs. f curves. K values for many compounds are not readily
oc
oc
p
available. Much research has been conducted to relate them to more com-
monly available chemical properties such as solubility in water (S ) and the
w
octanol–water partition coefficient (K ). The octanol–water partition coef-
ow
ficient is a dimensionless constant defined by:
C
K ow = octanol (2.27)
C water
where
C octanol = equilibrium concentration of an organic compound in octanol
C water = equilibrium concentration of the organic compound in water

K serves as an indicator of how an organic compound will partition between
ow
an organic phase and water. Values of K range widely, from 10 to 10 . Organic
7
−3
ow
compounds with low K values are hydrophilic (like to stay in water) and have
ow
low soil adsorption. There are many correlation equations between K and K
oc
ow
(or solubility in water, S ) reported in the literature. Table 2.6 lists the ones men-
w
tioned in an EPA handbook (EPA 1991). It can be seen that K increases linearly
oc
with increasing K or with decreasing S on a log-log plot. (Note: Values of K
w
ow
ow
for some commonly encountered COCs are provided in Table 2.5.) The follow-
ing simple correlation is also commonly used [4]:
K oc = 0.63K ow (2.28)
TABLE 2.6
Some Correlation Equations between K oc and K ow (or S w )
Equation Database
logK oc = 0.544 (logK ow ) + 1.377 Aromatics, carboxylic acids and esters, insecticides, ureas
or and uracils, triazines, miscellaneous
logK oc = −0.55 (logS w ) + 3.64
logK oc = 1.00 (logK ow ) − 0.21 Polycyclic aromatics, chlorinated hydrocarbons
logK oc = −0.56 (logS w ) + 0.93 PCBs, pesticides, halogenated ethanes and propanes, PCE,
1,2-dichlorobenzene
Source: [12].
Note: S w is the solubility in water, in mg/L.