EP A/600/A-97/026
USING ELEVATED TEMPERATURES TO ENHANCE IN
SITU REMEDIATION IN LOW-PERMEABILITY SOILS AND
GROUNDWATER
Civil Engineer, Ph.D. Gorm Heron
Department of Environmental Science and Engineering, Technical University of Denmark
National Risk Management Research Laboratory. U.S. Environmental Protection Agency
ATV MEETING
on groundwater contamination
VINGSTEDCENTRET
11-12 March 1997

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1. INTRODUCTION
Contamination of soil and groundwater by organies is recognized as a major threat to the
environment. Where contamination is severe and occurs deep or below buildings, excavation and
off-site treatment is impractical. In situ remediation is the only alternative to abandoning the area
and containing the spread of contamination.
The most commonly used remediation techniques are (1) pump and treat, (2) air sparging, (3)
vacuum extraction, and (4) stimulation of biological degradation. The physical-chemical
remediation techniques suffer from three major limitations. Firstly, when circulating water or air
through a geologic formation, the fluid will predominantly flow in the highly permeable layers,
rendering layers of low-permeable soil largely unaffected by the treatment. Often organic
contaminants bind stronger onto low-permeable, organic and clay-rich lenses and layers. Even if
the moving fluid totally cleans the ma jor part of the formation, the slow diffusion of contaminants
from low- to high-permeable layers may be rate-limiiing for the total clean-up (DiGiulio. 1992:
Gibson et al.. 1993). Secondly, limited volatility of the contaminants (low vapor pressure and
Henry's law constants) al the in-situ temperature may prevent a sufficiently rapid clean-up. even
when target areas are flushed with air. Thirdly, sorption of contaminants onto soil and aquifer
sediment may dramatically retard the movement with the lluid. Both the wet adsorption
coefficients (Kd) and the vapor sorption coefficient (K'\ are important parameters. For many
compounds, retardation factors in the range of 10 to several thousands may prevent efficient clean-
up. Recently, Davis (1997a) reviewed the effect of heat on the distribution of organies in soils and
groundwater.
This paper summarizes the effect of heating on the distribution of organies in the subsurface,
briefly reviews technologies used to inject heat in-situ, and finally illustrates the dramatic effect
of heating on contaminant removal rates using a controlled laboratory simulation. These results
arc currently submitted for publication elsewhere (Heron et al., 1997a: Heron et al. 1997b).
2. EFFECT OF TEMPERATURE ON PHYSICAL PROPERTIES OF CONTAMINANTS
In terms of basic physical-chemical parameters, the recovery of contaminants from soils and
aquifers may be controlled by the following: (1) vapor pressure, (2) solubility, (3) Henry's law
constant, (4) diffusion coefficients in water and air, and (5) sorption coefficients for dissolved and
vapor-phase contaminants, or the kinetic expressions related to these parameters. We will now
briefly review the importance of temperature for each parameter, supported by Table 1,
summarizing the temperature dependency as determined for TCE in a recent study (Heron et al.,
1997a).
2.1. Vapor pressure
The vapor pressure of an organic compound is a measure of its volatility when present as a free
phase liquid. Vapor pressure (Pv. measured in mmHg or Aim) varies strongly with temperature,
generally following the integrated form of the Claussius-Clapeyron equation. When AHra|>
(enthalpy/heat of vaporization) may be assumed constant over a narrow temperature interval.

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Table 1. Hypothetical enhancement factors for contaminant removal rates based on changes in the
physical properties of organic compounds with increasing temperature. Values are based on data
determined for trichloroethylenc in this study. Calculations are based on initial temperature of 20
°C. Data taken from Heron et al. (1997a).
In-situ temperature reached
Parameter
50°C
100aC
200°C
Solubility increase
1.1
1.4
-
Increased diffusion coefficient, air and water1
1.16
1.44
2.05
Henry's law equilibrium change
2.5
11
-
Increased vapor pressure
3.7
18
110
Decreased sorption coefficient K',. dry soiH
6
58
1360
Decreased sorption coefficient Kd, wet soil'
1.1
1.2
-
Decreased retardation in vapor phase, dry soil
6
57
915
1)	Using the power n = 1.5 in the temperature equation
2)	Assuming heat of sorption of - 46,2 kJ/mole
3)	Assuming heal of sorption of - 2 kJ/mole
integration yields:
Pv = C • cxp(-AHvap/RgT)
where C is an experimentally determined constant, Re is the natural gas constant, and T
temperature in Kelvins. Vapor pressures have also been approximated by other exponential
equations (CRC, 1994; Dean, 1985). These equations arc precise for temperatures below the
boiling point of the contaminant, but may be in error at higher temperatures (Heron et al., 1997a)
As an example, raising the temperature from 20 to 50, 100 and 200 °C would lead to an increased
vapor pressure for TCE by factors of 3.7, 18 and 110, respectively (Table 1). Thus, if free liquid
TCE is present, and the volatility is limiting the contaminant removal rate, the heating would lead
to equivalent enhancement factors, speeding up the removal significantly.
2.2 Solubility in water
When the in-situ temperature changes, the solubility of organies as free phases may also change.
There is no unique relationship between solubility and temperature. It was shown that the
solubility of TCE increases by 40% between 0 and 100 °C (Table 1). However, no general rule
exists for organic contaminants, but for compounds with a positive heat of solution in the 20-100
°C range, solubility may be significantly enhanced by soil heating, but probably not more than by
a factor of 2 {Heron et al, 1997a).

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2.3 Henry's law constant
When volatilization of contaminants from an aqueous phase governs the removal rate during
remediation, the air-water partitioning coefficient, the Henry's law constant H is the critical
parameter. Henry's law constant is defined as the ratio of the gas-phase concentration to the
dissolved concentration in equilibrium over a Hat water surface. Two forms are typically used, one
is the dimensionlcss Henry's constant 11, the other k„ has the unit of atm • nrVmol (Mackay & Shiu,
1981):
H = Cj/Cw or k„ = iycw where k„ = H • RgT
where CE and Cw have the units of mg/L or mol/irr, and Pv the unit of atm. Using this equation
for a saturated liquid/vapor system, it appears that Henry's law constant is equal to vapor pressure
divided by the solubility.
Henry's law constants for ITT. increase with temperature between 0 and 100 "C. Raising the
temperature from 20 to 50 and 100 C w ould icad to increases in Henry's law constants lot Hi.
by factors of 2.5 and 11, respectively (Table 1). Similar effects may be expected for other organic
compounds, since the Henry's law constant largely follows the increasing vapor pressure. Thus,
volatilization from a dissolved phase may be accelerated significantly by applying Heat. At
temperatures above 1(X)°C at atmospheric pressure, the use of Henry's law becomes questionable,
since the water will boil off and the soil start to dry out.
2.4 Diffusion coefficients in water and air
Diffusion in water or air may be limiting lor the removal rate of organics. For instance if free phase
contaminants are trapped in regions without water and gas movement (e.g. clay strata), the
diffusive transport through water or air to portions of the subsurface with moving fluid may
govern the overall removal rate.
Aqueous diffusion is typically four orders of magnitude slower than gaseous diffusion at 20 "C
(Peterson el al., 1988; Grifol & Cohen. 1994). Thus, in unsaturated soils, the apparent diffusion
coefficient D is strongly related to the saturation (Millington & Quirk, 196!):
D = D • 0 • 0 "2
cas	v'h>!
where D„ is the diffusion coefficient in air, and 0„,s and Gl0I are the gas-lllled and total porosity,
respectively. The temperature effect on D0 has been approximated by (Falta et al., 1992):
D„(T) = Do(T0) • (T/T,.)"
where n is an experimental constant, typically between 1 and 1.7 for aqueous diffusion and 1.5-1.6
for gaseous diffusion (Heron et al. 1997a). Assuming n = 1.5. raising the temperature from 20 to
50, 100 and 200 "C will increase the diffusion coefficient by factors of 1.16. 1.44. and 2.05.
respectively (Table 1). This is not a dramatic increase, and since the apparent diffusion coefficient

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also is strongly dependent on the moisture content, other physical changes such as drying of the
soil are supposed to dominate over the change in the diffusion coefficient at higher temperatures.
3.5. Sorption and retardation
Partitioning of organics onto soils affects remedial actions in several ways. Dcsorption rates affect
release of contaminants from target areas. Once released from the soil, the organic may be
removed by advection in either an aqueous or gaseous phase, and in both phases may be retarded
by adsorption onto soils. The moisture content of the soil and the soil gas arc important
parameters when discussing sorption, since vapor-sorption differs significantly from sorption in
an aqueous phase.
First we consider sorption in wet soils. The partitioning coefficient is given by:
Kd = c; / Cw
where the concentrations on the solid (Cs) and in the water (Cw) are in equilibrium. Assuming
constant heat of sorption, it was shown that (Heron et al., 1997a):
K(l = C • exp(-AHsor)1 /R,T)
Values for heat of sorption for saturated conditions are typically smaller (from 0 to -10 kJ/mole)
than for dry soils (from -20 to -65 kJ/mole for TCE vapor sorption onto dry soil minerals: Goss,
1992; Ong & Lion, 1991). If we assume -2 kJ/mole for TCE in groundwater and -46 kJ/mole for
TCE in dry soil (as shown by Heron ct al., 1997a), very different temperature dependencies are
seen (Table 1). Under saturated conditions, the Kd is reduced by factors of 1.1 and 1.2 for a
temperature increase from 20 to 50 and 100 °C. When we approach 100 °C, K(, is no longer a
reasonable parameter, since the soil will start to dry as the water boils off. In unsaturated and dry
soils, the mobile phase will be the soil vapor.
Equilibrium partitioning of organics involving vapor, soil moisture, and soil may be described by
the vapor sorption coefficient Kd:
K* = Cs / Cvap
where Cvap is the vapor phase concentration of the contaminant. With a heat of sorption of -46
kJ/mole, the partitioning coefficient decreases by factors of 6, 58 and 1360 when the temperature
is increased from 20 to 50, 100 and 2(X) °C, respectively (Table 1). Again, the stronger the
adsorptive forces, the stronger the temperature dependency.
Lowering of the Kd and Kd leads to a lowering of the retardation of the organic compound in
moving water or air, given by the retardation factor R:
R = 1 + K • p / 0
where K is the partitioning coefficient, p is bulk density, and 8 the porosity of the aquifer material.

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In dry soil, the R decreases by factors of 57 and 915 for temporalure increases from 20 to 100 and
200 (,C, respectively. Thus, recovery of contaminants through a vapor stream through dry soils
would be dramatically accelerated by heating if retardation in the vapor was limiting, even for a
moderately sorbing compound such as TCE. Even higher effects can be expected for heavier
contaminants such as oil components.
OVERVIEW OF REMOVAL ACCELERATING MECHANISMS
As shown in the previous section, especially increased volatility (vapor pressure and Henry's law
constant) and decreased adsorption (lower partitioning coefficients and retardation factors) would
lead to major changes in the behavior of organic compounds in soils and groundwater. However,
four other mechanisms during heating in-siiu may be equally imporiant (Heron et al.. 1997b):
-	heating groundwater may lead to formation of air/gas bubbles from dissolved gases such as
methane, oxygen, nitrogen and carbon dioxide and from vaporization of the water itself. Heating
lowers the solubility ol most gases in waiei. and bubble formation ma} lead u> n.csc.i.-.ed .Jvw ii.
and diffusion in pores or even channels.
-	when the boiling point of water is reached, the groundwater is converted into steam, which is
pushed out by the positive pressure generated. One mL of water occupies 1 mL as a liquid, but
1,700 mL as steam at 1 (K) °C. This 1,700 fold volume expansion leads to dramatic fluxes of steam
through the soil, which may potentially carry contaminants out of even very low-permeable soils
as shown by Heron et al. (1997b).
-	drying of soil layers opens up pores to vapor flow, and may expose free phase droplets present
as residual NAPL. For rcmediations based on air How (air sparging and vacuum extraction) this
may be a very important accelerating mechanism.
-	heating and drying may induce physical changes in clay minerals and fractures in clay layers,
greatly increasing the exposed surface area of such formations. This would lead to increased air
and water flow, and thus to enhanced removal of contaminants.
4. HOW TO APPLY HEAT TO THE TARGET VOLUMES
We now briefly review the technologies for heating soils and groundwater in-situ. Temperatures
reached during thermally enhanced in-situ remediation vary substantially, as reviewed below.
4.1. Thermal conduction using heat blankets or thermal wells
High temperatures (up to KXX) °C) may be reached using thermal blankets or wells, using electrical
heaters and simple thermal conduction through the soil from the hot areas into cooler areas (Iben
et al, 1995: Vinegar et aL 1993). The heat moves away from the blanket/well, and vacuum
extraction through slots or screens draws the hot air from the subsurface. Thermal desorption is
achieved by reaching temperatures of up to 300 "C up to 1 m away from the heal source. During

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move men i of desorbed contaminants towards the heat source, thermal destruction may lead to
complete contaminant removal in-situ. This technique is currently being tested in Houston, Texas
by Shell and General Electric. It's major disadvantage is the limited treatment volumes, caused by
the low thermal conductivity of most soils. Also application below the water table is questionable,
since large amounts of water would be vaporized before temperatures above 1(X) °C can be
reached.
4.2	Injection of hot air and steam
Injection of hot air or steam can be done with injection temperatures of up to 650 "C (Clarke et
al., 1994), but the temperature reached in the formation may be much lower due to the limited heat
capacity of air and steam. Injection of a hot fluids (air. steam or water) suffers from the major
disadvantage that the heat only can be injected directly into relatively permeable /.ones. Low-
permeable silt/clay layers will typically be heated solely by thermal conduction, which is a slow
process since soil is a good insulator (thermal conductivity typically between 0.25 and 3 W/mK:
De Vries. 1963). This problem was partly overcome by combining steam injection with resistive
healing of clay layers during the Dynamic Underground Stripping project, leading lo a ves v
succesful clean-up at a gasoline spill site (Newmark et al.. 1994).
Other field trials on steam injection have been less convincing (EPA. 1991; EPA, 1995c; EPA.
1995d; Lingenini & Dhir, 1992; Udell & Stewart, 1989). The major problem has been difficulties
m controlling the direction of steam flow and to get the target volumes up to steam temperature.
Another challenge is controlling the condensation front that moves ahead of the injected air or
steam. Generally, steam breakthrough to extraction wells and subsequent flushing of several pore
volumes is needed for succesful contaminant removal.
4.3	Hot water injection
Injecting hot water may lead to mobilization of free phase contaminants such as oils (Davis,
1997b). Some oils are denser than water at ambient temperature, but lighter at elevated
temperatures. Thus, heating oils may make them float to the top of the groundwater table for
removal by separation pumping. However, no good field evidence of this approach has yet been
published.
4.4. Low-frequency electrical (resistive) AC heating
Electrical heating techniques are based on resistive (Joule, ohmic) heating of the soil when an AC
cuirent is applied. Whereas silty and clayey deposits are low-permeable to fluids, they are typically
electrically more conductive than quartz sand due to higher amounts of clay minerals (electrically
conductive double layers) and to higher water contents due to stronger capillary forces. This fact
may be explored by preferentially heating fine-grained layers by low-frequency AC heating
(Gauglitz et al.. 1994; Newmark et al,. 1994; Phelan & Webb, 1994; Bueuner & Daily, 1995).
Resistive heating has been demonstrated to clean up a 3 m thick clay layer contaminated with
trichloroethylenc and perchloroethyiene by heating the clays in-situ to 100-105 "C (Gauglitz et al..
1994), and several other authors show that heating can be achieved (Aines et al., 1992; Bergsman

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et al., 1993; Ncwmark ct al. 1994; Buettncr and Daily, 1995). However, there is still a major need
to understand the processes taking place during heating and remediation. Also, electrical hazards
caused by the high currents applied pose challenges to the design of field equipment. Electrode
meltdown is another problem observed in the Held (Newmark et al.. 1994)
Soil resistivity is strongly dependent on soil water content, since the current predominantly (lows
in the soil water. Practically, this limits the use of low-frequency electrical heating to temperatures
below or close to the boiling point of water, since drying the soil will increase soil resistivity
dramatically and reduce current How (Chute & Vermeulen, 1988; Aines et al., 1992: Edclstein et
al. 1994).
4.5	Radio-frequency heating
Radio-frequency healing can be used to reach higher temperatures. The higher the frequency of
the applied current, the lower the effect of moisture content on the resistivity (Edeistein ct af.
1994). Therefore, radio-frequency (typically between 1 MM/ and 2.45 GH/.) electrical heating has
teen used foi heating msiI in-situ lo icmperaiuic.N uJ i4U C (Edclstein ct al.. 1994). 200 iSresty
et al., 1986), 250 "C (Snow et al.. 1993), and potentially as high as 400 °C (Chute & Vermeulen.
1988), However, the high frequency electrical heating requires expensive current sources and
matching networks (Edelstcin et al., 1994; EPA, 1995a; EPA, 1995b) and is less energy-efficient
than 50-60 Hz heating. Also, high electrical frequencies pose challenges to field equipment such
as temperature sensors, pressure transducers, tiltmeters, well material and wires. Temperatures
as high as 1(XX)"C have been observed at the injection antennas, where melting and corrosion of
brass and stainless steel have been reported (Snow ct al., 1993; Edclstein et al., 1994).
Once these engineering challenges are overcome, the high in-situ temperatures will lead to efficient
thermal dcsorptioti. high volatility of contaminants, and substantial steam drives out of all heated
soil layers. Snow et al. (1993) showed 97-99 % removal of volatile and semi-volatile organics
from silts, sands and gravel heated to al least 250 °C at Rocky Mountain Arsenal, Colorado.
Similar results were shown by Dev ct al. (1988. 1989) for BTEX and JP-4 fuel in a sandy soil at
Volk Air NCR, Wisconsin,
4.6	Microwave heating
Using microwaves (typically 2.45 GHz) injected by antennas may heat soil and groundwater in a
manner similar to the heating of foods in microwave ovens. Two approaches arc possible. One is
sfmilar to radiofrequcncy heating, where microwave heating is used in combination with vapor
extraction or air sparging (George et al.. 1992). Another approach is lo form a vapor blob below
the water tabic, where microwaves heat and vaporize water and contaminants at the interface
between vapor and water (Kearl & Ensley, 1996). The generated pressure drives water vapor and
contaminants to the screened antenna, where it is extracted and treated on-site. Both techniques
still lack field demonstration.

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30
40
50

2.5 g/d
0.35 s/d
0.13 ii/d
Days
The 2-dimensional box was spiked
with water and then left to
equilibrate lor 8 days prior to onset
of soil vapor extraction. Figure 3
shows the dissolved TCE
concentrations. The shape is
dominated by the fact that water and
TCE was added from the bottom
central screen, and kinetic
adsorption of TCE onto the soil
(Heron et al., 1997b).
Soil vapor extraction alone (days 0-
8) removed 2.4 » of TCE from the
box (7 9, of the added TCE). Clean
air entered through the top inlet
pons and quickly concentration* in
the outlet port dropped to very low
levels with a flux of about 0.13 g/d.
This flux was relatively constant
over a week of extraction, and
indicated thai it would take al least
250 days to clean the silty layer,
assuming that this flux could be
maintained. Practically, diffusion-
rale limitations and kinetic
desorption would lead to reduced
fluxes over time and supposedly to a
clean-up time of several years or
decades, showing that soil vapor
extraction would be inefficient as the
sole remediation technique for a
fine-grained, almost saturated layer
of this thickness (50 cm).
Figure 2. Power input, resulting soil
temperature and mass flux of TCE out of the
2D box (Heron et al.. 1997b).
At day 8, the electrical power was
switched on, and the box was heated
at a rate of 8 c,C7day until 80 °C was
reached on day 18, followed by
slower heating to 85 "C on day 21 (Figure 2). This resulted in dramatically increased fluxes of
TCE out of the central vent between days 10 and 20. dropping off towards a steady flux of about
0.35 g/d (Figure 2). The temperature was kept almost constant until day 35. where a total of 20
grams had been removed, and 15 gram of TCE remained in the box. The steady-state llux of 0.35
g/d reached indicated a total cleanup lime of at least another 50 days, assuming that a constant

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Day 0
Day 8
Day 21
Day 35
Day 45
Figure 3. Distribution of dissolved TOE (mg/L) in
water sampled from the 2D box (Heron el al.. 1997b)
Figure 4. Soil concentrations
of TCF (in (Jg/g) at the end
of the soil heating (Heron
eta!,. 1997b).
2(x:
m
\(h

I(X)

/—tttr^
o
1\X)
J
2 C2D
TCE flux could be maintained. At this
point, we decided to try to speed the
remediation up by raising the
temperature in the box further.
Then the power was increased, and 99-
100 °C was reached and maintained
through days 39-45 (Figure 2). This led
to another peak in the llux and later to
stabilization around 2.5 g/d. The power
was shut off on day 45, since the mass
balance indicated thai only trace
amounts of TCE remained in the soil
(Figure 3). The box was left to cool
down slowly over a 2 week period. The
soil vapor extraction was discontinued
on day 4K alter the llux of TCE out of
the box had dropped to below detection
limits, and finally soil samples were
collected for determination of TCE
levels in the treated soil. These showed
that the water content was unchanged
(due to wetting of the electrodes during
heating), and that only 70 mg of TCE
remained in the soil (Figure 4).
The TCE mass balance indicated an
overall recovery of 94.3 % by the SVB
system, and a remediation efficiency of
99.89J- with a residual TCE content of
70 mg in the soil compared to the initial
35.5 g on day 0 (Figure 4).

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This study demonstrated the effect of electric heating for healing up low-permeable soil for
enhanced removal of TCE. The cleanup lime was reduced dramatically compared to soil vapor
extraction alone when the silty soil was heated to 85 and 99 °C. As temperatures rise, the physical
properties of TCE and the soil change towards increased volatility, reduced sorption, and
increased diffusivity. In addition, a steam drive created when soil water boils pushes out the
surrounding soil vapor, leading to high TCE fluxes out of the soil. Since desaturation is not critical
for enhanced removal, electric heating may also be promising in shallow groundwater.
6. SUMMARY
Elevated temperatures may potentially be used to overcome the rate-limiting mechanisms during
in-situ remediation. Heating increases contaminant volatility and diffusiviiy. reduces adsorption
and tvtardation. and creates driving forces for soil vapor and contaminants. Applying the heat to
target subsurface areas poses several engineering challenges, and very few field irials have been
succesful m documenting efficient removal of organic contaminants. However, where these
difficulties were overcome, very promising results were found.
7. ACKNOWLEDGEMENTS
The experimental part of this work was financed by US EPA Cooperative Agreement No. CR
823908-01-0 entitled Joule Heating for DNAPL Remediation. It has not been subjected to
Agency review and therefore docs not necessarily reflect the views of the Agency, and no official
endorsement should be inferred. TNO Institute of Applied Geoscience supported the valuable
contribution of Marcus van Zutphen on this project.
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TECHNICAL REPORT DATA
1. REPORT NO.
EPA/600/A-97/026
2.
3
4. TITLE AND SUBTITLE
USING ELEVATED TEMPERATURES TO ENHANCE IN-SITU REMEDIATION IN LOW-
PERMEABILITY SOILS AND GROUNDWATER
5. REPORT DATE
March 11-12, 1997
6. PERFORMING ORGANIZATION CODE
Environmental Protection Agency
7. AUTHOR (S)
Gorm Heron, Ph.D.
NRMRL/SPRD - Ada
8. PERFORMING ORGANIZATION REPORT NO.
9. PERFORMING ORGANIZATION NAME AND ADDRESS
National Remediation Management Research Laboratory, EPA
Subsurface Protection and Remediation Division
P.O. Box 1198
Ada, OK 74820
10. PROGRAM ELEMENT NO.
11. CONTRACT/GRANT NO.
CR-823908
12. SPONSORING AGENCY NAME AND ADDRESS
EPA NRMRL/SPRD - Ada
P.O. Box 1198
Ada, OK 74820
13. TYPE OF REPORT AND PERIOD COVERED
14. SPONSORING AGENCY CODE
EPA/600/5
15. SUPPLEMENTARY NOTES
To be presented at the ATV meeting on groundwater contamination in Denmark on March 11-12, 1997
16. ABSTRACT Contamination of soil and groundwater by organice is recognized ae a major threat to the
environment. Where contamination is severe and occurs deep or below building, excavation and off-Bite
treatment is impractical. In-situ remediation is the only alternative to abandoning the area and containing
the spread of contamination.
The physical-chemical remediation techniques suffer from three major limitations. Firstly, when circulating
water or air through a geologic formation, the fluid will predominantly flow in the highly permeable layers,
rendering layers of low-permeable soil largely unaffected by the treatment. Often organic contaminants bind
stronger onto low-permeable, organic and clay-rich lenses and layers. Even if the moving fluid totally cleans
the major part of the formation, the slow diffusion of contaminants from low-to high-permeable layers may be
rate limiting for the total clean-up (DiGiulio, 1992; Gibson et al., 1993). Secondly, limited volatility of
the contaminants (low vapor pressure and Henry's law constants) at the in-situ temperature may prevent a
sufficiently rapid clean-up, even when target areas are flushed with air. Thirdly, sorption of contaminants
onto soil and aquifer sediment may dramatically retard the movement with the fluid. Both the wet adsorption
coefficients (Kj/and the vaapor sorption coefficient (K')a are important parameters. For many compounds,
retardation factors in the range of 10 to several thousands may prevent efficient clean-up.
This paper summarizes the effect of heating on the distribution of organics in the subsurface, briefly
reviews technologies used to inject heat in-situ, and finally illustrates the dramatic effect of heating on
contaminant removal rates using a controlled laboratory simulation.
17. KEY WORDS AND DOCUMENT ANALYSIS
A. DESCRIPTORS
B. IDENTIFIERS/OPEN ENDED TERMS
C. COSATI FIELD, GROUP
Remediation
groundwater
sorption
volatilization


18. DISTRIBUTION STATEMENT
Release to the public.
19. SECURITY CLASS(THIS REPORT)
Unclassified
21. NO. OF PAGES
14
20. SECURITY CLASS(THIS PAGE)
Unclassified
22. PRICE
EPA FORK 2220-1 (REV.4-77) PREVIOUS EDITION IS OBSOLETE

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