U.S. patent number RE33,102 [Application Number 07/218,154] was granted by the patent office on 1989-10-31 for removal of volatile contaminants from the vadose zone of contaminated ground.
This patent grant is currently assigned to The Upjohn Company. Invention is credited to James J. Malot, Melvin J. Visser.
United States Patent |
RE33,102 |
Visser , et al. |
October 31, 1989 |
Removal of volatile contaminants from the vadose zone of
contaminated ground
Abstract
Volatile contaminants are removed from the vadose zone of
contaminated ground by pumping volatilized contaminants from the
vadose zone using one or more vacuum extraction wells.
Inventors: |
Visser; Melvin J. (Portage,
MI), Malot; James J. (Dorado, PR) |
Assignee: |
The Upjohn Company (Kalamazoo,
MI)
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Family
ID: |
26912625 |
Appl.
No.: |
07/218,154 |
Filed: |
July 12, 1988 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
Issue Date |
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567972 |
Jan 4, 1984 |
4590760 |
|
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Reissue of: |
826713 |
Feb 6, 1986 |
04660639 |
Apr 28, 1987 |
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Current U.S.
Class: |
166/267; 166/370;
166/313; 405/128.3 |
Current CPC
Class: |
B09C
1/005 (20130101); E21B 43/00 (20130101); E21B
43/04 (20130101); E21B 43/38 (20130101) |
Current International
Class: |
B09C
1/00 (20060101); E21B 43/00 (20060101); E21B
43/02 (20060101); E21B 43/04 (20060101); E21B
43/34 (20060101); E21B 43/38 (20060101); E21B
043/00 () |
Field of
Search: |
;166/267,268,369,278,370,313 ;55/80,88 ;210/901 ;405/128,129 |
References Cited
[Referenced By]
U.S. Patent Documents
Foreign Patent Documents
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52-48202 |
|
Apr 1977 |
|
JP |
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52-52460 |
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Apr 1977 |
|
JP |
|
Other References
Thornton et al., J. Environ. Sci. Health A 17 (1), 31-44 (1982).
.
American Petroleum Institute Publication No. 4429, Mar., 1980.
.
EPA Handbook, 625/6-82-006, Jun. 1982, pp. 235-282. .
Ham, Robert K., "Large Elevation Landfilling for Refuse Disposal",
PublicWorks, Jan. 1970, pp. 92-95. .
Josephson, Julian, "Restoration of Aquifers" (undated). .
Recovery of Landfill Gas at Mountain View, EPA/530/SW/587d, May,
1977. .
Land Disposal of Hazardous Wastes, EPA 600/9-78-016, Aug. 1978, pp.
i-ix, 1-104 and 152-255. .
"Municipal Solid Wastes: Land Disposal", EPA 600/9-79-023a, Aug.
1979. .
Astel, Alice D. et al., "Estimating Vapor and Odor Emission from
Hazardous Waste Sites", Offsite Safety, pp. 326-330, (undated).
.
Rogoshewski, P. et al., "Remedial Action Technology for Waste
Disposal Sites", Noyes Data Corp. (1983). .
Amirtharajah, "Fundamentals and Theory of Air Scour", J. Env. Eng.
110, pp. 573-590, Jun., 1984. .
Hewitt et al., "Air Dynamics Through Filter Media During Air
Scour", J. Env. Eng. 110, pp. 591-606, Jun. 1984..
|
Primary Examiner: Kisliuk; Bruce M.
Attorney, Agent or Firm: Sears; Mary Helen Beery; Joanne
Parent Case Text
This is a continuation of application Ser. No. 567,972 filed Jan.
4, 1984 now U.S. Pat. No. 4,590,760.
Claims
The embodiments of the invention in which an exclusive property or
privilege is claimed are defined as follows:
1. A process for removing a not-naturally-occurring, volatile
liquid contaminant from a contaminated araa of the earth, wherein
the contaminated area of the earth has a subsurface water table and
a subsurface vadose zone above the water table, the contaminant
being present in the vadose zone, which comprises the steps of:
establishing a borehole extending downwardly from the surface of
the ground within the contaminated area;
placing a first conduit within said borehole so that a ring-shaped
zone is formed between the wall of said borehole and said conduit,
said conduit having a perforate lower portion located in the vadose
zone and spaced vertically above the water table so that fluids can
flow from the vadose zone into the interior of said conduit, said
perforate lower portion having an upper end and a lower end, said
conduit having an imperforate upper portion above the upper end of
said perforate lower portion.[.,.]..Iadd.; .Iaddend.
filling fluid-permeable first fill material into a lower portion of
said ring-shaped zone around said perforate lower portion of said
conduit and which extends to the upper end of said perforate lower
portion so that said first fill material will permit fluid readily
to flow into said perforate lower portion of said conduit;
filling a second fill material of low fluid permeability into an
upper portion of said ring-shaped zone around said imperforate
upper portion of said conduit, said second fill material being
effective to impede flow of air from the surface of the ground to
the lower portion of the borehole;
applying a vacuum to the upper end of said conduit effective to
induce flow of air and a gas containing vapor of said contaminant
present in said vadose zone into the lower portion of said conduit
and thence to the upper end of said conduit, the vacuum being
effective to cause vaporization of a substantial quantity of said
contaminant within the vadose zone around the borehole so that said
contaminant is removed from the ground in vapor form.
2. A process according to claim 1 including the additional step of
condensing water vapor and condensible contaminant present in said
gas and thereby separating the condensed liquids from the remainder
of said gas.
3. A process for removing a not-naturally-occurring, volatile
liquid contaminant from a contaminated area of the earth, wherein
the contaminated area of the earth has a subsurface water table and
a subsurface vadose zone above the water table, the contaminant
being present in the vadose zone, which comprises the steps of:
delineating the extent, thickness and contents of the contaminant
and also determining its direction and rate of spreading in the
vadose zone;
establishing at least one borehole extending downwardly from the
surface of the ground within the .[.contaiminated.].
.Iadd.contaminated .Iaddend.area;
placing a first conduit within said borehole so that a ring-shaped
zone is formed between the wall of said borehole and said conduit,
said conduit having a perforate lower portion located in the vadose
zone and spaced vertically above the water table so that fluids can
flow from the vadose zone into the interior of said conduit, said
perforate lower portion having an upper end and a lower end, said
conduit having an imperforate upper portion above the upper end of
said perforate lower portion.[.,.]..Iadd.;.Iaddend.
filling fluid-permeable first fill material into a lower portion of
said ring-shaped zone around said perforate lower portion of said
conduit and which extends to the upper end of said perforate lower
portion so that said first fill material will permit fluid readily
to flow into said perforate lower portion of said conduit;
filling a second fill material of low fluid permeability into an
upper portion of said ring-shaped zone around said imperforate
upper portion of said conduit, said second fill material being
effective to impede flow of air from the surface of the ground to
the lower portion of the borehole;
applying a vacuum to the upper end of said conduit effective to
induce only flow of air and a gas containing vapor of said
contaminant present in said vadose zone into the lower portion of
said conduit and thence to the upper end of said conduit, the
vacuum being effective to cause vaporization of a substantial
quantity of said contaminant within the vadose zone around the
borehole so that said contaminant is removed from the ground in
vapor form.
4. A process as claimed in claim 3 including the steps of pumping
contaminated water from below the water table; treating the
contaminated water to remove the contaminant therefrom; and then
recharging the decontaminated water to the ground.
5. A process as claimed in claim 3 including the step of treating
the volatilized contaminant discharged from the conduit by
mechanical, chemical or biological treatment to render it
harmless.
6. A process as claimed in claim 3 in which the contaminated area
comprises clayey subsurface media and in which the step of applying
said vacuum comprises first establishing a pressure of less than
about 10 mmHg in the conduit to dry out the clay around the conduit
and cause it to crack and become more permeable, and then applying
said vacuum to volatilize the contaminant, draw it into the well
and then discharge it above ground.
7. A process as claimed in claim 3 in which said perforate lower
portion of said .[.well casing.]. .Iadd.conduit .Iaddend.is located
directly above and close to the water table.
8. A process for decontaminating an underground vadose zone which
is located above the water table and is contaminated with a
volatile liquid contaminant which is percolating downwardly through
said vadose zone, which comprises:
establishing a vacuum extraction well comprising a well casing
having a perforate lower portion located in the contaminated vadose
zone and above the water table so that fluids can flow from said
contaminated vadose zone into said perforate lower portion of said
well casing, the area around said vacuum extraction well casing
above said perforate lower portion being substantially sealed to
impede flow of air around said well casing from the surface of the
ground to said perforate lower portion of said well casing;
applying a vacuum through said vacuum extraction well to said
perforate lower portion of said well casing, said vacuum being
effective to draw air through said contaminated vadose zone and to
volatilize liquid contaminant that is present in said contaminated
vadose zone above the water table and surrounding said perforate
lower portion of said well .[.caisng.]. .Iadd.casing .Iaddend.the
vapor containing the volatilized liquid contaminant being drawn
into said well casing and thence being transported to a location
above ground.
Description
BACKGROUND OF THE INVENTION
1. Field of the Invention
This invention relates to a process for removing volatile
contaminants from the vadose zone, also known as the zone of
aeration or, the unsaturated zone, that is, the zone between the
earth's surface and the underground water table.
In the following description, the term "volatile liquid
contaminant" shall mean the liquid phase of the contaminant and the
vapor phase in equilibrium therewith in the subsurface media.
Contaminant of the substrate ground with potentially hazardous
materials is a common problem facing industry, the government and
the general public. Often, as a result of spills, leakage from
storage facilities or surface discharges, contaminants enter
subsurface soil and/or rock formations. These contaminants
eventually percolate into the groundwater, thereby posing a health
threat to drinking water supplies. Various methods for withdrawing
and treating contaminated groundwater are well known and widely
practiced. However, methods for decontaminating substrate soil
and/or rock located in the vadose zone, above the water table, are
limited. Generally, the contaminated soil in the vadose zone is
excavated and removed. Alternatively, the contaminated soil can be
left in place so that the contaminants can be leached out by
percolating water and then the contaminated percolating water can
be removed and recovered after it has reached the water table. The
leaching of contaminants from the subsurface media is extremely
slow for many common contaminants because of their low solubility
in water and their absorption by soil and rock formations. As a
result, remedial measures, directing at cleaning up and protecting
the groundwater near a contamination site, must be performed for
many years or even decades. In addition, the prior methods are
ineffective for removing, from the vadose zone, contaminants having
a low solubility in water and/or a high affinity for soil, which
class of contaminants includes most of the hazardous pollutants
that affect groundwater. The present invention involves removing
volatile contaminants directly from the subsurface media in the
vadose zone above the water table.
2. Description of the Prior Art
Numerous techniques exist for removing gas that is formed naturally
in landfills and other constructed media. Circulation systems for
leaching the contaminants from contaminated media above the water
table have been designed, but they invariably require that the
leached contaminants enter the water table or aquifer and be
recovered by means of a water removal well and pump that draws
water from the saturated zone or aquifer (see, for example, Forte
et al, U.S. Pat. No. 4,167,973). In addition, it has been proposed
to remove contaminant vapors from contaminated underground areas by
means of a plurality of elongated perforated collection elements
installed in a large excavation (see Knopik, U.S. Pat. No.
4,183,407). However, this system is limited to removal of
contaminants from depths for which excavation is practical, usually
less than about 25 feet deep.
The present invention provides a method for removing volatile
contaminants from subsurface media, directly from any depth, within
the vadose zone, without effecting hazardous and expensive
excavation of a large amount of contaminated soil or rock. The
equipment used to perform the present invention can be conventional
equipment, most of which can be installed on the surface of the
ground. Thus, the equipment need not be specially manufactured or
installed within the contaminated area beneath the ground surface.
The equipment can be installed with minimal disruption of the
subsurface media. This is especially important in industrial
environments in which excavation may be detrimental to industrial
operations or the integrity of industrial structures in the area of
contamination.
SUMMARY OF THE INVENTION
The present invention includes the steps of directly removing
volatile liquid contaminant, which is precolating through the
substrate media, from the subsurface media in the vadose zone above
the water table and then collecting, treating or otherwise
disposing of the removed contaminant. According to the invention,
one or more wells are drilled into the subsurface media in the
contaminated area. The well is constructed so that fluids in the
vadose zone can flow into a well, whereas the liquid in the
saturated zone below the water table cannot substantially flow into
the well. The upper portion of the well is impervious, whereas the
lower portion of the well is perforate or open to the flow of fluid
thereinto. The lower portion of the well is surrounded by a
permeable material, such as gravel. The upper portion of the well
is filled with a material of low vapor permeability whereby to
inhibit leakage of air from the surface of the ground to the lower
perforate portion of the well. The upper end of the well is
connected to a suitable vacuum source, for example, an exhaust fan,
blower or vacuum pump, to create a relative pressure drop in the
well, thus indicating flow of volatile contaminants directly into
the perforate lower portion of the well. Once the contaminants are
in the well, they can be removed by means of the fan, blower or
vacuum pump, and/or by means of an optional submersible pump
located at the bottom of the well. The exhaust of the fan, blower
or vacuum pump, and/or the submersible pump, can be connected to a
suitable recovery, treatment and/or discharge system.
Thus, according to the invention, volatile contaminants are removed
from the vadose zone of a contaminated underground area by a series
of steps which comprises, firstly, establishing a borehole from the
surface of the ground within the contaminated area by drilling or
driving a borehole in any conventional manner. The borehole may
extend partway to the water table so that the bottom of the
borehole is located in the vadose zone and may be spaced above the
water table. However, the borehole and the hereinafter mentioned
perforate lower portion of the conduit may extend into the
saturated zone, in which case the perforate lower portion of the
conduit will be effective to draw contaminant from the vadose zone
and the vacuum in the conduit will be insufficient to draw a
significant amount of water from the saturated zone into the
conduit. However, if desired, a separate sampling device can be
provided in the borehole for obtaining samples of the groundwater.
A conduit or well casing is inserted in and is radially inwardly
spaced from the borehole so that a ring or annular zone is defined
between the wall of the borehole and the conduit. The conduit has a
perforate lower portion so that fluids can flow into the interior
thereof, whereas the upper portion of the conduit is imperforate.
The annular zone between the perforate lower portion of the conduit
and the borehole wall is filled with a loose, fluid-permeable,
first, fill material which extends substantially up to the upper
end of the perforate lower portion of the conduit. Thus, the
pressure drop between the perforate lower portion of the conduit
and the lower borehole wall portion opposed thereto will be low,
and the fluid-permeable fill material will easily permit fluid to
flow into the perforate lower portion of the conduit when vacuum is
applied to the conduit. The annular zone above the perforate lower
portion of the conduit is packed with a second fill material of low
permeability which is effective to impede flow of air from the
ground surface downwardly toward the lower portion of the borehole.
Thus, the flow of air from above ground vertically downwardly into
the conduit is minimized in order to increase the flow of the
volatilized contaminant from the substrate media into the conduit.
A vacuum is applied to the upper end of the conduit so as to draw
vapor of the contaminant present in the vadose zone into the lower
portion of the conduit, the contaminant vapor then flowing to the
upper end of the conduit, from whence it can be fed to other
equipment for treatment, recovery or discharge. The perforate lower
portion of the conduit is located in the vadose zone. When the
perforate lower portion of the conduit extends into the saturated
zone, no significant amount of groundwater is drawn from the
saturated zone into the conduit.
BRIEF DESCRIPTION OF THE DRAWINGS
FIG. 1 is a schematic view of a vacuum extraction system according
to the invention.
FIG. 2 is a partial cross-sectional elevational view of a vacuum
extraction well used in the system of FIG. 1.
FIG. 3 is a partial cross-sectional elevational view of a
modification of a vacuum extraction well.
DETAILED DESCRIPTION OF THE INVENTION
The invention is used to treat of substrate media in the vadose
zone V (FIG. 1), which media is contaminated with one or more
volatile liquid contaminants. The volatile liquid contaminant may
be percolating downwardly toward the water table, or it may be
relatively stationary in the vadose zone. For example, the
contaminants can be aliphatic and/or aromatic hydrocarbons,
halogenated hydrocarbons, or other volatile organic compounds
(VOCs). Such contaminants can be volatilized when subjected to
vacuum or a flow of air. The process of the invention is preferably
used for removal of contaminants having vapor pressures of at least
20 mmHg at temperatures of 23.degree. C. or less, and is most
preferably used for removal of contaminants having vapor pressures
of 100 mmHg at temperatures of 23.degree. C. or less. Contaminants
having lower vapor pressures can be removed, but the rate of
removing them is lower. The purpose of the invention is to
volatilize and remove the contaminants directly from the
contaminated zone so as to minimize the amount of contaminant that
enters the saturated zone, that is, the zone below the water table
WT (FIG. 1). The treatment is effected in situ without substantial
excavation or other disturbance of the subsurface media. The
invention is a cost effective procedure for removing contaminants
and it is effective to shorten the time required to clean up the
contamination. The invention is particularly good for removing
water-insoluble or sparingly water-soluble contaminants, but it is
also useful for removing water-soluble contaminants.
The invention is particularly concerned with removing the
contaminant from the vadose zone. However, the process according to
the present invention can and normally will be used in combination
with an additional system or systems for reclaiming contaminated
groundwater because not all of the contaminant will be removed by
the treatment according to the invention. Thus, for example, one or
more additional pumps can be provided to remove groundwater from
the aquifer, treat it and then recharge it into the aquifer after
removing the contaminant therefrom. The latter technique is well
known in the art.
When contamination of the subsurface media has occurred and it is
desired to remove the contaminants therefrom, the region of the
subsurface media that is contaminated will be delineated by
techniques which are well known in the art. For, example, test
borings can be made at selected locations and at selected depths in
and around the contamination site to determine subsurface geologic
conditions. In addition, chemical analyses of core samples taken
during the test borings for determining geologic conditions are
subjected to chemical assay to delineate the extent, thickness,
rate of spread and contents of the contamination in the unsaturated
zone.
After the contamination area has been delineated as discussed
above, the location or locations at which the installation of a
vacuum extraction well will be expected to be effective to remove
contaminant from the subsurface media will be determined, based on
hydrogeologic considerations. A vacuum extraction well will then be
installed at one or more of those locations. The vacuum extraction
well or wells may be installed in porous underground media,
preferably permeable, fine-grain materials such as silts and sands,
so that the well(s) will be effective to remove the contaminant
that is present in the underground media around the well.
If the subsurface media is relatively nonpermeable, such as clay,
the vacuum extraction well can be operated so as to dry the
surrounding clay so that it cracks and becomes more permeable
whereby contaminants can flow into the well.
Referring to FIG. 1, the vacuum extraction well 10 is connected to
a suitable vacuum source 11, such as an exhaust fan, blower or
vacuum pump. The discharge from the vacuum source 11 is connected
to any suitable system for collecting, treating, or otherwise
disposing of the removed contaminants. In the illustrated
embodiment of FIG. 1, the gas discharged from the vacuum source 11
is flowed through a condenser 12 wherein the water vapor and,
possibly, some or all of the volatilized contaminant that is
contained in the discharged gas may be condensed. The condensate
and gas are then flowed into a storage tank 13. The volatile
contaminant gas is then discharged into the ambient air through the
stack 14. When discharge of the volatilized contaminant into the
ambient air is not feasible because of environmental constraints or
the like, the contaminant can be treated in other known ways, such
as by adsorption, for example, by activated carbon, oxidation or
other chemical or biological treatment, to render same harmless. If
the contaminant is a useful substance, it can be collected for
future use. During operation of the vacuum extraction well, the
monitoring wells MW can be used to sample the subsurface conditions
around the vacuum extraction well and monitor the effectiveness of
the treatment.
Referring to FIG. 2, the vacuum extraction well 10 is comprised of
a borehole 21 which can be dug in the ground by any well-drilling
method suitable for penetrating the subsurface media that is
present at the contamination site. A vertical well casing or
conduit 22, which is of smaller diameter than the borehole 21, is
installed substantially coaxially within the borehole so as to form
an annular zone 23 therebetween. The upper portion 22A of the pipe
22 is imperforate, whereas the lower portion 22B of the pipe is
perforate so that fluid can flow therethrough from the subsurface
media into the interior of the pipe. The lower portion 23B of the
annular zone between the lower portion 22B of the pipe 22 and the
borehole wall is packed with a loose, fluid-permeable, first, fill
material 24, such as gravel, sand or rock, so that the pressure
crop between the lower perforated portion 22B of the pipe and the
borehole wall will be small, whereby fluid present in the region
surrounding the lower portion of the borehole wall can easily flow
into the perforate lower portion 22B of the pipe 22. The upper
portion 23A of the annular zone between the upper portion 22A of
the pipe 22 and the borehole wall is filled with a low-permeability
material, such as soil, clay or cement. In the illustrated
embodiment there is shown a bentonite seal layer 26 made of
bentonite balls expanded with water, which seal layer is located
close to the upper end of the perforate lower portion 22B of the
pipe 22. On top of the bentonite seal layer 26, there is provided a
layer 27 of expansive grout which extends from the bentonite seal
layer to the surface of the ground. The purpose of the seal layer
26 and the layer 27 of low permeability material in the upper
portion of the borehole is to impede flow of air from the surface
of the ground to the lower portion 22B of the borehole and to
direct the vacuum to zones of higher contamination.
When the vacuum source 11 is turned on, if the subsurface media is
a porous permeable material the absolute pressure in the vicinity
of the perforate lower portion 22B of the pipe 22 is reduced and,
thereby, flow of air, contaminant vapor and liquid is induced
through the contaminated media and into the perforate lower portion
of the pipe 22. The rate of volatilization of the contaminant is
thereby increased and the equilibrium concentration of the
contaminant in the vapor phase is also increased. Thus, the
contaminant is drawn into the perforate lower portion of the pipe
22 and is brought to the upper end of the pipe 22 whereat it can be
treated, collected or otherwise disposed of.
If the subsurface media is relatively nonporous, impermeable,
water-bearing clay, it is necessary to apply a sufficiently high
vacuum to dry out the clay around the borehole to cause it to crack
and thereby become more permeable so that the contaminant can flow
into the pipe 22. Thus, when the vacuum source is turned on, it is
preferable to establish a pressure of less than 10 mmHg to dry the
wall of the borehole. Once the borehole wall has been dried, the
operation can proceed in the same manner as described above.
The source of the air that flows into the perforate lower portion
22B of the pipe 22 can be the air that is naturally present in the
substrate media or that infiltrates into the surface media from the
ambient air at the ground surface. In addition, air for
volatilizing the contaminant can be artificially provided by
drilling air supply wells or making excavations in the area
surrounding the vacuum extraction well 10 in order to promote the
flow of fresh air into the subsurface media. The recharging of
fresh air into the subsurface media can be passive or active. In
passive recharging, an open well or excavation is provided to allow
fresh air to enter in response to a pressure gradient. In active
recharging, fresh air is pumped under superatmosphere pressure into
the subsurface media near the vacuum extraction well 10.
In many installations, liquid water, aqueous contaminant and liquid
contaminant will accumulate in the perforate lower portion 22B of
the pipe 22 because some of the water that is percolating through
the subsurface media toward the water table will be drawn into the
pipe 22 by the vacuum. In order to remove this water and any other
liquid that may become present in the perforate lower portion 22B
of the pipe 22, a submersible pump 28 can be installed close to the
bottom of the pipe 22. When the submersible pump 28 is in
operation, water and other liquids, including possibly liquid
contaminants, are pumped out of the well 10 in the liquid phase.
The liquid can be treated in order to remove the contaminant, for
example, they can be flowed directly into the tank 13. The pump 28
can be turned on and turned off in response to the liquid level in
the pipe 22, as determined by liquid level probes (not shown) in a
conventional manner.
The objective of the vacuum extractions of the contaminant from the
vadose zone is to minimize the amount of contaminant that enters
the aquifer. The most effective zone of accomplishing vacuum
extraction of the contaminant is the zone directly above and close
to the water table because in that zone, the width of the zone
around the vacuum extraction well in which a significant vacuum is
present is maximized. Also, the contaminant may tend to accumulate
at the surface of the water table when the contaminant is of low
water solubility. Thus, it will be preferred to locate the bottom
of the perforate lower portion 22B of the pipe 22 close to, but
spaced vertically above, the water table WT in the subsurface media
being treated. The distance between the bottom of the perforate
lower portion 22B and the water table will be determined based on
the zone of influence of the vacuum extraction well and the
location of the contaminated area.
The vertical height of the upper portion 23A of the annular zone
that is packed with the fill material of low permeability, will be
chosen to minimize as much as possible the infiltration of air from
the ground surface into the lower portion of the borehole.
In another modification of the invention, as illustrated in FIG.3,
the borehole may be drilled into the saturated zone and a pump may
be installed to pump water therefrom through a first passageway,
while simultaneously a perforate zone may be provided in the
borehole communicating with the vadose zone to draw vapor therefrom
through a second passageway separate from the first passageway.
Thus, the same well can be used as a well for monitoring and
removing ground water, and for separately removing volatilized
contaminant.
The method according to the invention is effective to remove
substantial qualities of volatile contaminant that is present in
the subsurface media above the water table whereby to minimize the
amount of the contaminant that enters the groundwater. The nature
and amount of the contaminant that is present in the subsurface
media, the vapor pressure of the contaminant, the characteristics
of the subsurface media and the number and sizes of the vacuum
extraction wells that are used, are factors that affect the total
treatment time and overall effectiveness of the treatment. Although
it may be necessary to carry out the treatment for a long period of
time, it is likely that the treatment time will be shorter than the
time that would be required if the only treatment performed was to
pump water from the aquifer and reclaim it. The invention will be
particularly advantageous and effective at the early stages of
treating the contamination site because it can achieve relatively
rapid removal of relatively large quantities of the contaminant. It
may also be effective to reduce the spreading of the contaminant in
the subsurface media. Thus, if the nature of the contamination
requires the use of one or more removal wells for removing
contaminated water from the aquifer, separating the contaminant
from the water and recharging the decontaminated water into the
aquifer, the amount of actually contaminated water that must be
pumped out and treated can be reduced so as to make it possible to
use a smaller pump, a lesser number of pumps and/or a shorter
treatment time period for removing contaminated water from the
aquifer.
Although a particular preferred embodiment of the invention has
been disclosed in detail for illustrative purposes, it will be
recognized that variations or modification of the disclosed
apparatus, including the rearrangement of parts, lie within the
scope of the present invention.
* * * * *