Geoscience Reference
In-Depth Information
Chapter 8
Selected Research Findings: Contaminant
Partitioning
In the previous chapters of Part III, we discussed various aspects that affect the
partitioning of contaminants of anthropogenic origin among the liquid, solid, and
gaseous phases in saturated and partially saturated porous media. The partitioning
process controls the fate of contaminants in the subsurface, defining their redis-
tribution and transformation. This chapter presents selected research findings that
illustrate various aspects of contaminant partitioning in the subsurface. We stress
that, although many examples are included here, this chapter does not cover the
entire
spectrum
of
contaminant
partitioning
phenomena
that
occur
in
the
subsurface.
8.1 Partitioning Among Phases
Under natural conditions, contaminants often reach the earth's surface as a mixture
of (potentially) toxic chemicals, having a range of physicochemical properties that
affect their partitioning among the gaseous, liquid, and solid phases. As a conse-
quence, contaminant retention properties in the subsurface are highly diverse.
Contaminants may reach the subsurface from the air, water, or land surface.
As an introductory example, we consider gasoline (a common and universally
used petrochemical product comprising a mixture of about 200 hydrocarbons with
different properties) to illustrate contaminant redistribution among phases in
relation to their environmental behavior. The recent model of Foster et al. (
2005
)
provides an excellent approach for assessing differential volatilization, dissolution,
and retention of various gasoline hydrocarbons in the environment. Based mainly
on their volumetric composition, relevant properties (vapor pressure, water solu-
bility, octanol/water partition coefficient K
ow
), environmental/human hazardous
aspects (e.g., toxicity), and persistence (in water, soil, sediments), the authors
grouped gasoline hydrocarbons into 24 blocks with a density increasing from
0.564 to 0.837 g/mL. Hydrocarbons were grouped primarily into structural clas-
sification including alkanes and alkenes with normal, branched, or cyclic structure;
aromatics with
one
or
two
rings;
and
the
number
of
carbon atoms
in
the
