In Situ Remediation Technologies - Dealing with Contaminated Sites: From Theory Towards Practical Application - page 954

Combining Eqs. ( 21.2 ), ( 21.7 ) and ( 21.11 ) leads to:

K d
K d

m = (21.12)

The value of the solid-gas partitioning coefficient is dependent on temperature
as well as moisture content in the unsaturated zone. When the moisture content is
reduced in the unsaturated zone, the percentage of the absorbtion site susceptible
to contamination at the soil surface will increase and therefore the value of K d
will increase. For biological degradation of contaminants in the unsaturated soil, a
minimal moisture content is necessary, which is comparable to about 20% of the
pore volume (Koorevaar et al. 1983 ). At these conditions no strong increase of the
K d value was found for several contaminants.
From the equilibrium equations above it becomes clear that, although no spe-
cific information is known about the soil characteristics, a good indication can be
obtained from the physical/chemical properties of the organic contaminants on the
preferential position of the contaminants in the contaminated site. As a consequence,
regulators and site operators can already determine from initial site samples whether
pure product can be expected.
In Fig. 21.1 an overview of the relations between the different phases is
presented.
From the equations one can determine if the largest fraction of the contaminant
is present in the liquid, the gas, the solid phase or as pure product. Regulators and
site operators can preselect with these equations a specific remediation technology,
as most technologies are directed to remediate only one specific phase in the soil
system. If pure product can be expected, source treatment technologies are of inter-
est. If high concentrations of vapour or dissolved concentrations are high, the In
Situ technologies for treatment in the path of spreading are of interest. If a receptor
is at risk via soil gas or groundwater contamination, specific technologies can be
selected.

Water

S

K d m

NAPL

P s

Fig. 21.1 Relations between
four different phases in which
organic contaminants in soil
can be present

K d '

Air

Solid