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Soil vapor extraction (SVE) is a cost-effective remediation
process for the soil of unsaturated zone contaminated with
volatile organic compounds (VOCs). This process can be applied
with simple basic equipment without the confinement of site
geographical features, and can be used in-situ for the purpose
of lowering the disturbance of the site. In order to predict and
evaluate the removal efficiency of the SVE process under humid
conditions, this study investigates the transport phenomena in
soil during SVE actices and find out how the VOCs removal will
be influenced by the soil moisture content.
The soil collected from the riverside of Hsin-Tien Hsi was used
in this study. From batch tests, the adsorption isotherm and
linear partition coefficients of toluene vapor to the soil were
obtained. The data revealed that the sorption capacity was the
highest for the oven-dried soil, and with the increase of soil
moisture content, the sorption capacity deceased. It may result
from the competition between water and toluene in the sorption
sites on the mineral surface. Same results have been reported in
the lerature. In the venting experiments,
toluene was induced into soil columns of various moisture
content by pulse inputs. The results revealed that the slow
sorption effect was most obvious in air-dried condition
(moisture content=1.6%). Also the removal efficiency in air-
dried condition was the lowest (16.74~36.25%). In the columns
simulating capillary zone and saturate zone, the breakthrough
time was quicker and removal efficiency was higher (50.02
~58.54%) than the air-dried column because water occupied the
sorpti sites and obstructed the diffusion of toluene into soil
pores. The one-dimension
advection-diffusion model weree contents. The results showed
that the model did not fit the data well due to the slow
equilibration equilibrium phenomena proven with the lower
toluene concentration peak and obvious tailings. In the columns
with higher moisture contents, the measured toluene
concentration peak moved faster than the model prediction
possibly due to the formation of stagnant saturated regions and
mo confined gas channels and flow path in soil columns. It
revealed that soil water will promote the removal efficiency in
this pulse input experiment by blocking the diffusion path for
toluene. But if the contaminant was originally spread into the
stagnant moistened zone, the same effect will decrease the
removal efficiency.
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