United States
Environmental Protection
Agency
Robert S. Kerr Environmental
Research Laboratory
Ada OK 74820
Research and Development
EPA/600/S2-91/016 July 1991
<3rEPA Project Summary
Forced Air Ventilation for
Remediation of Unsaturated
Soils Contaminated by VOC
Jong Soo Cho
Many cases of soil vacuum extrac-
tion (SVE) applications In the field have
been reported, but very few systematic
studies about physical and chemical
processes In soil air are found. Param-
eters which were expected to control
the removal process of VOCs from con-
taminated soil during the SVE opera-
tion were studied by means of numerical
simulations and laboratory experiments
In this project
Experimental results of SVE with soil
columns In the laboratory Indicated that
the removal efficiency of VOCs from
soil columns was a complicated func-
tion of air flow and the hydrogeometry
Inside. The partition process between
air and the immobile liquid was not an
equilibrium one, and the interfacial mass
transfer varied with the residual amount
of VOCs In the soil. Additional experi-
ments under various conditions should
be conducted to obtain further insight
Into the SVE process.
Two computer models were devel-
oped to study soil air and VOC move-
ment during the SVE process. The first
one was an analytical approximate
model which could be used for the simu-
lation of air movement in the SVE op-
eration with multiple wells In
homogeneous soil media. The second
one was a numerical model in three-
dimensional geometry which used a fi-
nite difference solution scheme. A
simple pneumatic pump test was con-
ducted, and parts of test data were used
for the validation of the simple analyti-
cal model.
This Project Summary was devel-
oped by EPA'* Robert S. Kerr Environ-
mental Research Laboratory, Ada, OK,
to announce key findings of the research
project that Is fully documented In a
separate report of the same title (see
Project Report ordering Information at
back).
Introduction
Fuel leakage and spills are the most
frequent sources of soil and ground-water
contamination at service stations and un-
derground storage tank areas. A large por-
tion of released hydrocarbon infiltrates the
subsurface and remains bound under cap-
illary pressure as a residual immiscible
phase liquid. The residual hydrocarbon
serves as a continuous source for ground-
water contamination. Therefore, the recla-
mation of the contaminated aquifer should
include removal of the long-term con-
tamination source. The cleanup of soil
contaminated by Volatile Organic Contami-
nants (VOCs) is generally an expensive
operation due to the high cost associated
with excavation, transportation, and dis-
posal. Classic methods such as soil re-
moval, forced percolation, encapsulation,
or trenching are frequently impossible or
prohibitively expensive, especially in the
midst of an industrial or residential area.
An alternative method to remediate soils
is the use of the soil vacuum extraction
(SVE) system. This process has proven to
be inexpensive and effective for the cleanup
of soil and ground water contaminated by
solvents and volatile components of petro-
leum products. The cost of installation and
Printed on Recycled Paper
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operation of an SVE system is usually
lower than the cost of other methods. An-
other major advantage is that this method
is an in-situ process. The contaminated
soil remains in place and is not excavated
and disposed of in other locations. The
SVE system is also used for the control of
methane gas migration from landfills. Meth-
ane and carbon dioxide, which are gener-
ated by microbial decomposition of organic
materials, can migrate a long distance from
the landfill and build up to explosive levels.
The SVE wells, sometimes with interdic-
tion walls, are installed to prevent the mi-
gration of methane gas. In spite of many
field applications, very few scientific or sys-
tematic studies have been reported. There-
fore, the design of the SVE system has
been mainly dependent on experience and
rough estimations. Sometimes, prototype
or pilot-scale systems are used to obtain
design parameters such as well depths,
well spacings, and extraction rates.
The objective of this project was to
investigate the movement of VOCs in soil
air during the SVE process. Several physi-
cal and chemical processes are involved
in the movement of VOCs in soil air, in-
cluding convective and diffusive transport,
interfacial mass transfer between immis-
cible phases, and biological/chemical trans-
formations. Physical and chemical
properties of soil and VOCs are expected
to control these processes. The ultimate
goal of this project was to obtain knowl-
edge on relationships among the various
properties and processes of VOC trans-
port in soil air. These relationships were
integrated in computer models. This report
includes laboratory experiments and field
tests of SVE in relatively simple systems.
The model development procedures are
also included in this report.
Process of Soil Vacuum
Extraction
The basic principle of SVE is very
simple. Air flow is induced in the subsur-
face by a pressure gradient applied through
vertical wells or horizontal trenches. The
flowing air sweeps out VOCs by vaporizing
highly volatile components from soil pores,
and the contaminated soil air is collected
by extraction wells. Effluent air from ex-
traction wells is often treated by off-air
treatment systems, i.e., an activated car-
bon tank or catalytic converters. A typical
SVE system consists of air pumps or blow-
ers connected to a series of wells located
in contaminated soil. The bwer pressure
inside the extraction well generated by
pumps causes soil air to move to the well.
Sometimes air injection wells are added
for the further control of air flow. VOC
movement in convective and diffusive
modes is considered as the main process
of chemical transport during the SVE op-
eration. When there is an induced pres-
sure gradient, the bulk phase of soil air
moves and carries a large amount of VOCs
in the convective transport mode. Espe-
cially in the close vicinity of wells and
trenches, a large pressure gradient is de-
veloped and the convective transport domi-
nates the movement of VOCs. At remote
areas from wells, the pressure gradient
becomes very small. VOC transport in these
remote locations from the wells is expected
to be slow because of the diffusive trans-
port. In addition to the convective and dif-
fusive movements, VOC transport in soil
air during SVE is expected to be influ-
enced by several other processes includ-
ing the partition process among gas, liquid
and solid soil matrices, and biological/
chemical transformations. Biological/chemi-
cal transformation processes of VOCs were
not investigated in this project.
Soil Air Flow
The VOC concentration in soil air is
usually low, and the changes in thermody-
namic and transport properties of soil air
due to the concentration change are not
significant. Therefore, air flow is consid-
ered to be independent of the VOC con-
centration in soil air and treated explicitly
from VOC transport. In cases where
changes of physical and chemical proper-
ties due to the high concentration of VOCs
in soil air are significant, iterative or updat-
ing computational procedures should be
used to solve the coupled problems.
Three basic equations are considered
in the description of air flow: the mass
balance equation of soil air, the flow equa-
tion due to pressure gradients, and the
equation of state. The mass balance of soil
air is expressed by the equation of conti-
nuity.
t
= -VpaV
(1)
where the
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NA-cAV-4>.DVcA
(5)
where c is the concentration of the compo-
nent A in soil air, V is the velocity vector of
air flow, $ is the air-filled porosity in soil,
and D is the diff usivity.
The mass balance of the component A
in soil air becomes
(6)
dt
-VcAV + V$a DVcA
where S, is the source/sink term of soil air.
The mass balance of the component A
in the immobile phase becomes
9CA
dt
•S,
(7)
where q>/ is the pore volume occupied by
the immobile phase, CA is the concentra-
tion in the immobile phase, and S/ is the
source/sink term for the immobile phase.
The source/sink terms both in the mass
balance of component in soil air and the
immiscible phase include the interfacial
mass transfer and biological/chemical trans-
formations.
Several parameters are used in the
description of the VOC movement and
therefore are needed to obtain solutions of
the air flow and VOC transport equations.
Properties of soil and VOCs should be
measured for the accurate design of the
SVE operation on the specific site. Most
thermodynamic and transport properties of
VOC components in air can be obtained
from reported data. These properties may
change depending on the operating condi-
tion of the SVE. The property changes
caused by operating conditions sometimes
give considerable variations in the effi-
ciency of the SVE. Thermodynamic and
transport properties of VOCs in various
conditions can be estimated from theoreti-
cal and empirical relationships. These pa-
rameters are the soil air permeability,
molecular weight of soil air, viscosity of
gas mixture, diffusivity in gas mixture, va-
por pressures and aqueous solubilities of
VOCs.
Interfacial Mass Transfer
One of the empirical correlations for
the interfacial mass transfer between im-
miscible phases is the first order kinetics
expression. The rate of mass exchange
between immiscible phases is expressed
by the mass transfer potential and the
mass transfer coefficient. The difference of
the concentration at equilibrium and the
actual concentration in the main body is
defined as the mass transfer potential. The
mass transfer rate is expressed as
nA-KQ(CA-cA) (8)
where CA is the concentration of A at
equilibrium, CA is the actual concentration
in the main body of fluid, and KQ is the
mass transfer coefficient. The mass trans-
fer coefficient, KQ , is expected to be a
function of Reynolds' number, Schmidt's
number, and the air saturation, 6., which is
the ratio of the air-filled porosity to the total
porosity of soil.
KQ - KQ (Re, Sc, 9. ) (9)
Effect of Parameters
Analytical solutions in one-dimensional
systems have been obtained for the soil air
flow and contaminant transport equations
under simplifying assumptions. Those so-
lutions were applicable for analysis of
simple soil column operations. Effects of
parameters on the VOC movement have
been studied through simulations and com-
parisons with soil column experiments.
Analysis of SVE Processes
The pressure distribution calculated
from the analytical solution of the air flow
equation showed variations with location
inside a one-dimensional soil column, but
was not a function of the air permeability at
steady state. The pressure and correspond-
ing velocity distributions obtained from the
linearized and nonlinear equations showed
discrepancies between calculated values.
The maximum difference in pressure distri-
butions inside the column was about 20%
when the ratio of the inlet pressure, p^, ,
and the outlet pressure, p^ , was 0.6. But
the corresponding air flow velocity showed
a significant difference between calculated
values from the linearized and nonlinear
equations. When the pressure ratio was
0.9, the maximum difference was about 10
%, and it was about 70 % at the location of
the lowest pressure when the pressure
ratio was 0.6. Errors in the air flow velocity
generate errors in the estimation of the
convective movement term in the transport
equation. Therefore, one should be very
careful when the linearized equation is
used.
Air and liquid saturations in soil pores
were expected to have significant effects
on both the air flow and VOC transport.
The relative permeability of soil air was a
function of the air saturation. If the liquid
saturation, including the water and immis-
cible nonaqueous phases, was high, then
the relative permeability became so small
that a large pressure drop was expected.
The effect of the air saturation on the
transport of the VOC impacted the
diffusivity, as did the interfacial mass trans-
fer from the immobile phase to the air flow.
The liquid saturation was also considered
to determine the effective interfacial area
for the mass transfer. As the liquid satura-
tion increased above the residual satura-
tion, the mass transfer coefficient was
expected to increase due to the increased
interfacial area between contacting phases.
After passing the maximum point, the in-
terfacial area decreased, and so did the
mass transfer coefficient. The change of
contacting area was considered to be a
complicated function of the hydrogeometry
inside soil pores and was expected to vary
continuously as the removal process of the
VOC and soil water continues. Additional
efforts should be made in this area of
research. Systematic studies in the labora-
tory and field should be conducted to gain
better knowledge of the process.
Temperature Effect on the
Removal Efficiency
To investigate the temperature effect
on the performance of the SVE process,
the soil column experiment was simulated
at three different temperatures. In compar-
ing property changes at different tempera-
tures, the largest differences were found in
vapor pressures. At a 15°C increase of
temperature in the ambient condition, the
vapor pressure of TCE doubled. The major
contributing factor to the performance of
the SVE process at increased temperature
was the vapor pressure increase. The re-
moval rate doubled when the operating
temperature increased 15°C. In future stud-
ies, it may be worthwhile to consider in-
creased temperature operation.
VOC Removal Rate
Measurements
One of the controlling processes in SVE
is the partitioning among gas, liquid, and
solid soil phases. When the convection
dominates the transport of VOCs and its
rate is fast, local equilibrium assumption is
not accurate; and a kinetics model seems
to be more appropriate to describe parti-
tion processes. Experimental investigations
of two parameters, the air flow rate and the
liquid distribution including the nonaque-
ous phase liquid and water, on the re-
moval rate of VOCs from soil columns are
presented.
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So/7 Column Experiments
Nine soil columns made of 2-inch,
Schedule 80, PVC pipe were used. Each
column had a soil-packed section 28 to 30
cm bng and two additional empty sections
with a cap on each end. Brass fittings were
attached on the top and bottom sections of
the columns. Both 1/4 inch I.D. plastic and
copper tubings were used; plastic tubings
were used where VOC did not contact.
The Oil Creek sand was packed in the
columns. The sand was white and very
uniformly sized with very small amounts of
organic content on the surface. These col-
umns were set up in a constant tempera-
ture room. Pure toluene was used as a
VOC and was applied on top of the soil-
packed section of each column drop by
drop through a hypodermic syringe to mini-
mize the disturbance of soil packing. The
same method was used for water applica-
tion to control water content. After applica-
tion of each liquid, a 24-hour equilibrium
period was set to achieve uniform distribu-
tion of liquid. The air flow rate was moni-
tored with a rotameter and adjusted as
necessary with two needle valves. The
vacuum pressure and the pressure drop
through the column were measured with
manometers. An in-house vacuum line was
attached to the column for the vacuum
source. The vacuum pressure and corre-
sponding air flow rate fluctuated about 10
% from the set point. Air was saturated
with moisture by passing it through water
baths before it entered the columns to
minimize the water content change in the
soil. Samples of effluent air from each
column were taken directly by a gas-tight
chromatograph syringe and injected into
an HP 5840A gas chromatograph equipped
with an FID. A 6 ft, 1/4 inch O.D. custom
packed stainless steel column (Supelco,
EPA Method 602) was used for analysis of
toluene concentration in air. Nitrogen
served as the carrier gas at a flow rate of
36 ml/min. The injector and FID tempera-
tures were set at 110°C and 150°C, re-
spectively. The column oven temperature
was fixed at 90°C. A specialty gas mixture
(Blend 3, Scott Specialty Gas) was used
as a standard for calibration.
Results and Discussion
Two major parameters investigated in
this experiment were the air flow rate and
liquid phase contents of the immiscible
nonaqueous VOC and water in soil. The
effluent concentration decreased as the
time passed even in the case where only
pure toluene was applied. This decrease
of effluent concentration suggests that the
interfacial mass transfer is a function of
residual liquid contents inside soil pores.
Also these decreasing rates of effluent
concentrations varied with respect to the
air flow rate. At a lower flow rate, the
effluent concentration change was slower
than at the higher air flow rate. These
trends were maintained through different
water content and distributions inside soil
columns. To verify the VOC and water
distribution effects on the removal, the ef-
fluent concentration changes at different
initial liquid VOC and water were investi-
gated. Throughout these experiments, the
amount of toluene applied on each column
was far above the water solubility, and,
therefore, toluene existed as an immiscible
nonaqueous liquid. The vapor pressure
was expected to be that of pure toluene.
Nevertheless, the effluent rate was seri-
ously affected by the water content in the
soil. Increasing water contents reduced
the removal rate. This may be due to the
entrapment of residual VOCs inside soil
pores by water and thereby reducing con-
tacting area between the air and VOC
phase. However, this could not be verified.
Even though the air flow rate and the
liquid distribution of VOCs and water were
distinctive parameters verified through
these experiments, it was not possible to
obtain quantitative correlations among
them The main reason was that through-
out these experiments, mass balances of
VOCs and water could not be checked.
Another unexpected result was the non-
uniform distribution of VOCs and water
inside soil columns. It was found that liq-
uids, including toluene and water, moved
upward as air flowed up from the bottom of
the column and accumulated in the upper
part of the soil packed section of the col-
umn. Redistribution of liquids and experi-
mental results suggest the necessity for a
new design of soil column and experimen-
tal procedures which include the control
and measurement of liquid content
changes.
Removal Rate Model
A similarity of physics involved in the
moisture removal from a wet solid by dry
air and the VOC removal from soil pores
by uncontaminated air suggests the same
conceptual model. The moisture removal
model consists of the constant rate period
and the falling period. The constant rate
period is at the first stage of the drying
process in which the moisture removal rate
remains constant and is mainly controlled
by external factors like air flow, tempera-
ture, and the moisture content in the air.
The falling rate period represents the sec-
ond stage of the removal process in which
the removal rate decreases as the mois-
ture content reduces after a critical point.
In this stage, the moisture removal rate is
controlled by internal factors such as the
liquid diffusion, the capillary flow of liquid,
or the flow by shrinkage of solid pores. The
capillary movement of liquid water due to
the change of the suction potential by
evaporation of moisture inside pores is
expected to control the drying rate of sand
soil or granular materials by air flowing
through pores. The moisture removal rate
is approximated by first order kinetics. The
removal rate of VOCs from soil pores can
be expressed with the same concepts of
physical process. During the first stage
after air flow begins, the removal rate from
soil pores remains constant until the VOC
content is reduced to a critical value.
dt
when *A
(critical amount)
(10)
At the second stage, after the critical point
of the VOC content has been reached, the
removal rate decreases as the VOC con-
tents decreases. It is expressed by a first
order kinetics model of the removal of
VOC from the soil pores.
dt
where K-|
-Si
-, and
(11)
tow-
(CA,c-CA,e)
est obtainable amount of liquid VOC under
the given operating conditions. The solu-
tion of the above equation for the falling
rate period can be obtained.
t_(CA.c-CA.e)|n(CA.c-CA,e)
(CA r - CA o)
The semilogarithmic plot of Mf c M> e/
vs. t should give a straight line and the
slope of the curve is related to the constant
rate. The constant rate S,, and the coeffi-
cient, K,, are expected to be complex func-
tions of the liquid saturation, 6^ and various
operating conditions.
K,-K, (Re, Sc, 0X) (13)
Soil Air Flow Model with
Superpositions of Analytical
Solutions
The development of a three-dimensional
analytical approximate model to simulate
the air flow during the SVE operation and a
simple pneumatic pump test conducted on
an aviation gasoline-contaminated site are
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presented. The model used a superposition
of the analytical solutions obtained from
potential theory in a three-dimensional
space. This model is only applicable to
homogeneous media. Pneumatic pump
tests were conducted to obtain soil air flow
characterization around an air injection and
vacuum extraction well in relation to a field
demonstration project for bioremediation.
The result revealed the importance of the
pneumatic pump test prior to the design of
a full scale operation. A part of the test
results was used for the validation of the
model.
Analytical Solutions
At steady state, the equation describ-
ing the pressure distribution of soil air is
V K. p Vp - 0
(14)
Three appropriate boundary conditions are
a constant pressure boundary, like soil
surface exposed to the atmosphere, a zero
flux boundary for the impermeable layer,
and the continuous flux condition at the
interface between different permeability lay-
ers.
The superposition of exact solutions is
possible only for the linear equations. By
applying the Kirchoff transformation on the
above equation as follows,
dm -KaPorm -*a
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Very important information on design
of an SVE system can be obtained from
pneumatic pump tests. Design parameters
in the SVE system should include the zone
of influence in which the pumps can pro-
duce the sufficient airflow. Estimation from
the measurable vacuum pressure can
cause overestimation of the radius of the
zone of influence. The major factor in de-
termining the zone of influence should be
the pressure gradient and corresponding
air flow. The pumping efficiency could be
measured from the tests. A single high
vacuum pumping well does not have a
larger zone of influence than the low
vacuum pumping well because a large
pressure gradient exists only in the vicinity
of the well. The SVE system with multiple
low vacuum wells may be more efficient
than one with a single high vacuum well.
Combined operation of extraction and in-
jection wells could induce horizontal air
flow, but still a large vertical flow is ex-
pected in the vicinity of wells. Therefore,
the system should be carefully engineered
to obtain reasonable efficiency. A tightly
covered soil surface may help to induce
more horizontal flow. Additional field tests
are suggested to measure the pressure
distribution of the operation with a tightly
covered soil surface and also with various
lengths and locations of well screens.
Three-Dimensional Finite
Difference Model
A mathematical model was developed
for the simulation of the soil vacuum ex-
traction process in field scale. This model
consisted of a soil air flow equation, the
contaminant transport equation and the
mass balance equation of residual hydro-
carbon inside soil matrices. The air flow
equation was transformed to a Laplace
type equation to obtain the soil air pres-
sure distribution and the flow velocities.
The calculated air flow velocities were used
in the transport equation to describe the
convective movement of VOC. In addition
to the convective movement, the transport
equation included the diffusive movement
and the interfacial mass transfer between
the air and the residual hydrocarbon con-
tacting the flowing air. The mass balance
equation for the residual hydrocarbon was
also used. The numerical method to solve
these differential equations with boundary
conditions was the finite difference method
in a three-dimensional space domain and
the unsteady state time process.
Finite Difference Solutions
The soil air flow arrives at steady state
quite rapidly after the SVE system is initi-
ated by pumping the air into/out of the
subsurface. The contaminant movement
usually is a non- steady state problem until
all the contaminant mass is removed from
the system. Therefore, it is reasonable to
assume that the air flow is at steady state
during the operating period. In this project,
a finite difference method with central spa-
tial difference scheme was adopted to solve
this air flow equation. Replacing the differ-
ential equations with the difference opera-
tors results in the difference equations for
the air flow equation. By applying the above
finite difference operator on all the interior
nodal points, excluding the boundary points,
w, where specific conditions are assigned,
the total number of linear algebraic equa-
tions becomes (M-1) x (N-1) x (L-1) - w.
The number of equations increases rapidly
as the nodal points increase. For example,
100x100x100 system generates 100,000
simultaneous algebraic equations which
need a tremendous amount of computa-
tional time. In this project, the point Jacob!
iterative method was selected to solve the
equations because it uses considerably
less CPU memory than the direct solution
method, allowing the large physical prob-
lems to be simulated. Additional refine-
ment adopting various preconditioner and
accelerator schemes is needed to make
the program faster and more stable.
Several finite difference schemes have
been developed to solve these convective
diffusion equations of the VOC transport.
In this project period, two simple schemes
have been tested, the explicit method and
the alternating direction implicit (ADI)
schemes; only the explicit scheme was
implemented in the program. The advan-
tage of the explicit scheme over the implicit
scheme is that each node is computed
explicitly and the computations need less
memory and processor time. The disad-
vantage is that the selection of time step
increment is severely dictated by the sta-
bility conditions. Usually, the ADI scheme
is unconditionally stable and has second-
order convergence error. One would have
to invert a set of three tridiagonal matrices
for each time step with the ADI scheme.
Computer Implementation
Very often, the modeling of fluid flow
and contaminant transport in the subsur-
face is dictated by availability of computer
resources. Because of limited computa-
tional resources at Kerr Laboratory, the
point Jacob! method for the air flow equa-
tion and the explicit scheme for the VOC
transport equation were selected. Both
methods require less memory and compu-
tational time; but because of limited time
step allowed, they may not be suitable for
the long period of simulation. Currently,
the algorithms and controlling program dis-
cussed above are implemented in FOR-
TRAN 77 on an Apollo DN4500 using Unix
system V as the primary operating system.
The sampling array used by this model is
101x101x51 which calculates to 520,251
physical nodes. Given this amount of
nodes, the program requires approximately
10 megabytes (MB) of memory which is
not suitable for personal computers.
Through implication, a larger model would
require even greater memory to function.
Provided with the main program is a
postprocessor program which is for graphi-
cal display of data generated by the main
program. It is specifically designed with an
XWindows interface and will require an
XWindows server be available to run the
postprocessor.
Conclusions and
Recommendations
From analyses of experiments and
model simulations, very valuable informa-
tion could be obtained. The observation of
simulated results based on soil column
experimental conditions showed several
physical and chemical properties influenc-
ing the efficiency of the SVE operation.
Among VOC chemical properties, the va-
por pressure was the most sensitive factor
that controlled the efficiency of total opera-
tions. Air flow rate and liquid distribution
were very important parameters which con-
trolled the removal rate of VOCs from soil
columns. A conceptual model was pro-
posed to describe the evaporative process
of VOCs from the residual liquid in soil
pores. The pneumatic pump test gave very
important information for design of SVE
systems, including the zone of influence,
soil characterization, and pumping efficien-
cies. Two computer models for soil air flow
and VOC transport in the SVE system
were developed. The analytical solution
model developed was very simple and easy
to use. Simulations of pneumatic pump
tests with this model revealed that the
model generated reasonable results and
could be used as an initial design tool. A
fully three-dimensional finite difference
model was developed. Various solution
methods have been tried, and explicit
schemes were selected to reduce the com-
putational time and memory requirements.
A graphical postprocessor was attached to
enhance the visualization of output results.
The proposed future works are as fol-
lows: A large number of studies on mass
transfer have been reported in engineering
literature, but very few pertain to soil sys-
tems. Soil particles and pore sizes are not
uniform, and the Reynolds' number is usu-
ally less than 0.1 in soil systems. The
extrapolation of empirical correlations to
unmeasured operating conditions is not
desirable, and further studies are required
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to obtain more precise correlations suit-
able for soil systems. More experiments
are suggested with modified columns and
procedures for quantitative analyses. The
proposed model for VOC removals from
soil pores needs to be verified through
additional experiments. More research on
the enhancement of SVE by increased
temperature is also needed to achieve bet-
ter efficiency of the SVE operations. Pneu-
matic pump tests are recommended under
various operating conditions before full
scale implementations of SVE systems.
Tracer gas tests will help further. A main
reason for the lack of field scale model
developments is the expense of the model
validation with field scale data. It is very
costly to perform tests for the model vali-
dation, but this is a very necessary step. A
simple pneumatic pump test, like the one
reported in this project, will give very im-
portant information for model validation and
optimal design of the SVE system. Addi-
tional refinement and validation of the ana-
lytical solution model are necessary for
further field applications. The finite differ-
ence model is still in the developmental
stage and needs a rigorous validation
through numerical experimentations and
comparison with field data. In addition to
the validation, alternative schemes should
be tested to accelerate the computation.
.S. GOVERNMENT PRINTING OFFICE: I«W2 - 64H-080/402H
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The EPA author, Jong Soo Cho (also the EPA Project Officer, see below), is with
Robert S. Kerr Environmental Research Laboratory, U.S. EPA, Ada, Oklahoma 74820.
The complete report, entitled "Forced Air Ventilation for Remediation of Unsaturated
Soils Contaminated by VOC," (Order No. PB91-181750/AS; Cost: $17.00, subject to
change) will be available only from:
National Technical Information Service
5285 Port Royal Road
Springfield, VA 22161
Telephone: 703-487-4650
The EPA Project Officer can be contacted at:
Robert S. Kerr Environmental Research Laboratory
U.S. Environmental Protection Agency
Ada, OK 74820
United States
Environmental Protection
Agency
Center for Environmental Research
Information
Cincinnati, OH 45268
BULK RATE
POSTAGE & FEES PAID
EPA PERMIT NO. G-35
Official Business
Penalty for Private Use $300
EPA/600/S2-91/016
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