Method of removing contaminants from contaminated soil in situ

A method of removing contaminants from a contaminated soil area in situ comprises the steps of placing a barrier in engagement with the exposed surface of the contaminated soil area, sealing the barrier around the periphery of the contaminated soil area and reducing the pressure beneath the outer layer of the barrier to draw the contaminants out of the soil. The barrier is comprised of an outer fluid impermeable layer and an inner fluid permeable layer. The edges of at least the outer layer of the barrier are sealed by digging a trench in the uncontaminated soil beyond the periphery of the contaminated soil area, inserting the edges of the barrier into the trench, refilling the trench and compacting the fill against the ends of the barrier. A liberating fluid may be injected into the soil beneath the contaminated soil area through a plurality of conduits inserted into the soil at acute angles.

BACKGROUND OF THE INVENTION 
The present invention relates generally to a method of removing 
contaminants from contaminated soil in situ and, more particularly, to 
such a method that employs a fluid impermeable barrier on the surface of 
the contaminated soil and a vacuum for drawing out the contaminants. 
Increased environmental awareness has prompted concern over harmful and 
often irreparable contamination of natural resources. Contamination of 
soils and the underlying water table have posed particularly acute 
problems in recent years. Many sites are contaminated by accidental spills 
and dumping of hazardous liquids, such as organic solvents and 
hydrocarbons, which become absorbed by the soil and reside temporarily or 
permanently in the soil's interstices. 
Contaminated soils such as these are generally useless to support 
vegetative and animal life, and often pose a threat to the surrounding 
ecosystems. In addition, an even more dangerous and pervasive threat 
exists in the possibility that such contaminants may flow hydrodynamically 
downward through the soil to the water table, rendering the immediate 
water unusable and spreading rapidly to contaminate surrounding water 
resources. 
In the past, labor and capital intensive and time consuming excavation, 
decontamination and recovery procedures were employed to clean the soil 
and remediate the site. Such procedures often required digging shafts and 
underground conduits and flooding the contaminated area with suitable 
solvents. In addition, such excavation and flooding generally required 
drilling a bore so that the solvents and contaminants could run off into a 
reservoir for subsequent removal. Moreover, canopies and extensive exhaust 
systems were required to minimize atmospheric pollution or to remove 
contaminatd vapor flowing out of the contaminated soil as a result of the 
decontamination process. Moreover, while such procedures functioned 
reasonably well, they were not equally applicable to contamination in 
soils of different density, moisture contents and transmissivity. 
The present invention overcomes many of the disadvantages inherent in the 
methods of decontamination described above by providing a method of 
drawing out contaminants from the soil while minimizing atmospheric 
leakage and hydrodynamic downward flow. In addition, the present invention 
may be employed in conjunction with soil areas of greatly varying density, 
moisture content and transmissivity. The methods of the present invention 
are greatly simplified over the prior art and, therefore, may be applied 
to contaminated soil areas quickly, easily and efficiently, with the 
result of considerable cost and time savings. 
SUMMARY OF THE INVENTION 
Briefly stated, the present invention is a method of removing contaminants 
from a contaminated soil area in situ. The method comprises placing a 
barrier in engagement with the exposed surface of the contaminated soil 
area. The barrier is comprised of an outer fluid impermeable layer and an 
inner fluid permeable layer. The barrier is sealed around the periphery of 
the contaminated soil area and the pressure beneath the outer layer of the 
barrier is reduced to draw the contaminants out of the soil. The 
invention, in one embodiment, further comprises inserting a plurality of 
conduit means into the soil at acute angles, at least a portion of each 
conduit means extending beneath at least a portion of the contaminated 
soil area. One end of each conduit means extends upwardly beyond the soil 
surface and is secured to a source of liberating fluid. Each conduit means 
includes a plurality of outlets for injecting the liberating fluid into 
the soil beneath the contaminated soil area. The liberating fluid is then 
passed through the conduits to liberate the contaminants from the 
contaminated soil area.

DESCRIPTION OF PREFERRED EMBODIMENTS 
Referring to the drawing, wherein like numerals indicate like elements 
throughout, there is shown in Fig. 1 a sectional view through a portion of 
ground showing a contaminated soil area 12. The contaminated soil area 12 
may have been created by spilling, dumping or otherwise releasing a 
contaminant or contaminating substance, such as a contaminating fluid, on 
the exposed surface of the soil. Upon release, such a contaminating fluid 
generally permeates the underlying soil, moving downward and/or radially 
outward to create a contaminated soil area 12, which may generally be 
bowl-shaped or arc-like in cross section, as shown in FIG. 1. The degree 
to which the contaminating fluid permeates the soil and spreads downward 
and/or radially outward from the site of release varies depending upon the 
permeability and moisture content of the soil, the viscosity of the 
contaminating fluid, the air and soil temperature and other factors. 
However, it should be clearly understood that the methods of the present 
invention are equally applicable to any size contaminated soil area 12 and 
to any type of contaminated soil. 
The present invention comprises a method of removing contaminants from a 
contaminated soil area 12 in situ. A barrier or geocomposite 10 is placed 
in engagement with the exposed surface 18 of the contaminated soil area 
12. The barrier or geocomposite 10 is comprised of at least two layers, as 
shown in FIG. 3. The outer layer 14 of the geocomposite 10 is impermeable 
to fluids and may be comprised of a polymer material, such as 
polyethylene. Such fluid impermeable materials are produced commercially 
in many forms and thicknesses by many companies, such as the National Seal 
Company, the Phillips Fibers Corp., Gundle Lining Systems, Inc., and J. P. 
Stevens Co., Inc. In the presently preferred embodiment, the thickness of 
the outer layer 14 is about 80 mil. However, the thickness of the fluid 
impermeable outer layer 14 may vary and is determined based upon the ease 
of handling desired, the soil surface to be covered, the strength of a 
vacuum pressure to be exerted beneath the fluid impermeable layer 14, as 
will be hereinafter described, and other factors, which will hereinafter 
become apparent. 
The inner layer 16 of the geocomposite 10 is highly permeable to the 
contaminants to be withdrawn from the contaminated soil area 12. 
Preferably, the inner fluid permeable layer 16 is comprised of a mesh 
material, such as fabric, netting, screening or webbing. Such materials 
are commercially available from many sources, including the Phllips Fibers 
Corp., Polyfelt, Inc., the Tensar Corp. and ATP Corp. The type of material 
and the size openings of the mesh depends upon the transmissivity of the 
soil present in the contaminated soil area 12. Generally, the inner layer 
16 is formed of a material having a fine mesh when the soil present in the 
contaminated soil area 12 is a fine particulate soil, such as silt or 
clay. Conversely, when the soil in the contaminated soil area 12 is 
coarse, such as gravel or sand, an inner layer 16 having a coarse mesh is 
employed. It may be desirable to utilize inner fluid permeable layer 16 
materials of different mesh size in tandem and/or overlapping to cover 
soils of varying characteristics in the contaminated soil area 12. The 
materials utilized for the fluid permeable inner layer 16 may also vary 
depending upon the transmissivity of the contaminants in the contaminated 
soil area 12, the temperature and other weather conditions and other 
characteristics of the contaminants. For example, to draw out a 
contaminant of high viscosity from the contaminated soil area 12, it may 
be preferable to employ a fluid permeable inner layer 16 with a coarser 
mesh size than if the contaminant to be drawn out were of a lower 
viscosity. It will be appreciated by those skilled in the art that the 
present invention is not limited to a particular mesh material or class of 
such material, but that any material with an appropriately sized mesh may 
be employed. 
The overall thickness of the geocomposite 10 may vary, depending upon 
variations in the thickness of the outer layer 14 and the inner layer 16. 
In a preferred embodiment, as shown in Figs. 1 and 3, the overall 
thickness of the geocomposite 10 is less than one inch. It will be 
appreciated by those skilled in the art that for certain applications, the 
thickness of the geocomposite 10 may be greater or less than one inch, and 
that the present invention is not limited to a barrier or geocomposite 10 
of particular thickness. 
The geocomposite 10 is placed in engagement with the exposed surface 18 of 
the contaminated soil area 12 over the entire region to be decontaminated. 
As previously indicated, the size and shape of the contaminated soil area 
12 varies, depending upon the type of soil present, its water content, the 
type of contaminants and other factors. The overall size and shape of the 
geocomposite 10 correspondingly varies so that the geocomposite 10 is 
sized and shaped to cover and extend at least slightly beyond the entire 
contaminated soil area 12. Typically, the contaminated soil area 12--and 
thus the geocomposite 10--is generally circular in a top plan view, 
because fluid contamination of soil areas typically spreads out in a 
generally regular circular pattern from its point of release. The size and 
shape of the contaminated soil area 12 may be determined by employing 
probes (not shown) or other types of test apparatus (not shown) in a 
manner well known in the art. It will be appreciated by those skilled in 
the art that the present invention is not limited to a geocomposite of a 
particular size or shape. 
After the geocomposite 10 has been placed on the exposed surface of the 
contaminated soil area 12, the peripheral edges of the geocomposite 10 are 
sealed around the periphery of the contaminated soil area 12 as shown in 
FIG. 1. In the presently preferred embodiment, the peripheral edges of the 
geocomposite 10 are sealed by digging a trench in the uncontaminated soil 
surrounding the contaminated soil area 12 and inserting the edges of at 
least the outer fluid impermeable layer I4 of the geocomposite 10 into the 
trench. The trench is then refilled and the fill is tightly compacted 
against the fluid impermeable outer layer 14. It will be recognized by 
those skilled in the art that the depth of the trench necessary for 
sealing the geocomposite 10 will vary depending upon the characteristics 
of the soil and the size of the contaminated soil area 12. Typically, a 
trench on the order of about one foot to about four feet deep is 
preferred. The width of the trench varies, depending upon the type of soil 
and the manner in which the soil may be compacted for sealing the 
geocomposite 10. 
To remove the contaminants from the contaminated soil area 12, the pressure 
beneath the outer layer 14 of the geocomposite 10 is reduced to draw or 
pull out the contaminants by a suction force. In the present embodiment, 
the pressure beneath the outer barrier layer 14 is reduced by a pumping 
source or vacuum pump (not shown), the negative pressure end of which is 
attached to one end of a conduit or pipe 20. The other end of the pipe 20 
extends beneath the outer fluid impermeable layer 14 to provide fluid 
communication between the vacuum pump and the area beneath the outer fluid 
impermeable layer 14. The negative pressure or vacuum applied by the 
vacuum pump preferably exerts a suction force on the surface of the 
contaminated soil area 12 of between five and thirteen pounds per square 
inch. In this manner, contaminants are drawn out of the surface 18 of the 
soil, which is in engagement with the inner fluid permeable layer 16 of 
the geocomposite 10. The contaminants pass through the inner fluid 
permeable layer 16 and are vacuumed off through the pipe 20 to a container 
(not shown) for processing, storage or transportation. The inner fluid 
permeable layer 16 permits removal of the contaminants while holding the 
soil in place. 
It will be apparent to those skilled in the art that the time period 
required for such negative pressure or vacuum applied to the soil in this 
manner to draw out of the contaminants in the contaminated soil area 12 
will vary. Such period of time depends upon the overall size of the 
contaminated soil area 12, the volume of the contaminants, the 
transmissivity of the soil, the transmissivity of the contaminant or 
contaminants and other factors apparent to those skilled in the art. For 
example, it generally takes less time to draw high transmissivity 
contaminants from the soil than the time it takes to draw lower 
transmissivity contaminants from the same soil. Correspondingly, it 
generally takes less time to draw the same contaminants from high 
transmissivity soil than from low transmissivity soil. Each application of 
the present invention must be evaluated on a case-by-case basis to 
determine when the contaminants have been removed. 
The contaminated soil area 12 may be periodically analyzed by using one or 
more probes (not shown) or other known test apparatus (not shown) to 
determine the presence or absence of the contaminants in the soil. 
Alternatively, if the volume of the contaminant released is known, the 
volume of the recovered contaminants may be analyzed and compared to the 
known volume to determine when an acceptable percentage of the contaminant 
or contaminants have been recovered. 
While in many applications the above-described method is adequate for the 
removal of many contaminants, it will be recognized by those skilled in 
the art that certain soils, certain environmental and/or ecological 
circumstances and certain contaminants may require additional means to 
facilitate contaminant removal. For example, a soil contaminated with high 
viscosity contaminants in cold weather conditions, which further hinder 
the transmissivity of the contaminants through the soil, may prove more 
difficult to decontaminate. In such cases, it may be preferable to 
facilitate contaminant removal by decreasing the viscosity of the 
contaminants or by combining the contaminants with a liberating fluid 
having a higher transmissivity than the contaminants. In addition, 
exigencies may exist whereby the time for contaminant removal is to be 
preferably accelerated. In such a case, again, it may be preferable to 
facilitate contaminant removal by utilizing a liberating fluid. 
The present invention further comprises injecting a liberating fluid 
beneath the contaminated soil area 12. In the embodiment shown in FIG. 2, 
a plurality of conduit means or pipes 24 are inserted at spaced locations 
into the soil, at least a portion of each pipe 24 extending beneath at 
least a portion of the contaminated soil area 12, so that a liberating 
fluid may be injected into the soil to help liberate the contaminants from 
the soil. In this manner, stubborn contaminants, such as contaminants that 
may adhere to the soil substrate, and other types of contaminants may 
react, dissolve, or may become otherwise released from the soil and drawn 
out by the vacuum as described above. 
In the present embodiment, it is preferred that the pipes 24 each have a 
plurality of outlets 26 along at least the portion of the pipes 24 
extending beneath the contaminated soil area 12, and be inserted directly 
beneath the contaminated soil area 12 at acute angles with respect to the 
surface of the soil. 
One end of each pipe 24 extends upwardly beyond the exposed surface of the 
soil 18 in the present embodiment preferably beyond the periphery of the 
contaminated soil area 12 and beyond the sealed edges of the geocomposite 
10. The ends of the pipes 24, which extend above the surface of the soil, 
are secured to a source of liberating fluid (not shown). The liberating 
fluid source provides liberating fluid under pressure, which passes 
through the pipes 24 and out of the outlets 26. The outlets 26 beneath the 
contaminated soil area 12 are positioned so that liberating fluid passing 
therethrough flows in an upward direction as indicated by arrows 30. The 
vacuum assists in drawing the liberating fluid upward through the 
contaminated soil area 12. 
The depth to which the pipes 24 are inserted depends upon the permeability 
and water content of the soil in the contaminated soil area and, hence, 
the depth of the contaminated soil area 12. Clay, for example, is not 
highly permeable and the pipes 24 may be inserted to a depth of about one 
to five feet. Gravel, on the other hand, is highly permeable and the pipes 
24 may be inserted to consierably greater depths. One skilled in the art 
can determine the appropriate insertion depth in view of the depth of the 
contamination within the contaminated soil area 12. 
In the present embodiment, it is preferred that the liberating fluid pumped 
through the pipes 24 for injection into the soil beneath the contaminated 
soil area 12 is heated air or steam. However, any other fluid suitable for 
liberating contaminants from the soil could be employed either alone or in 
combination with the heated air or steam. 
It is presently preferred that the method of placing a geocomposite 10 in 
engagement with the exposed surface 18 of the contaminated soil area 12 
sealing the geocomposite 10 around the periphery of the contaminated soil 
area 12 and reducing the pressure beneath the outer layer 16 of the 
geocomposite 10 to draw the contaminants out of the soil is the first step 
of soil decontamination. If this method is not effective in removing a 
particular contaminant from the soil or is not fast enough, the second 
step comprises installing the pipes 24 and injecting heated air through 
the pipes 24 and out through the outlets 26 into the soil beneath the 
contaminated soil area 12 to liberate the contaminants therein. If the 
injection of the heated air is not effective or fast enough in liberating 
a particular contaminant from the soil, the next step comprises injecting 
steam through the pipes 24 and out through the outlets 26 into the soil 
beneath the contaminated soil area 12 to liberate the contaminants 
therein. However, as will be appreciated by those skilled in the art, the 
liberating fluid could be of any other composition suitable for 
facilitating removal of contaminants from the soil. 
Furthermore, the liberating fluids injected into the soil may be varied or 
may be alternated depending upon the characteristics of the soil and the 
characteristics of the contaminants. The amount of liberating fluid 
injected into the soil may also vary depending upon the characteristics of 
the soil and/or the characteristics of the contaminants. 
From the foregoing description, it can be seen that the present invention 
comprises a method of removing contaminants from a contaminated soil area 
in situ. It will be appreciated by those skilled in the art that the 
present invention may be embodied in other specific forms without 
departing from the spirit or the central attributes thereof and, 
accordingly, reference should be made to the appended claims, rather than 
to the foregoing specification as indicating the scope of the invention.