Enhanced gradient soil and groundwater remediation method

An enhanced pressure gradient remediation system (10) for decontaminating a contaminated volume of soil incorporates at least one extraction well (40) operated independently or in conjunction with at least one injection well (12). The injection well (12) is employed to inject steam, or ambient or heated air, into the soil, and extraction probe (40) extracts fluids, contaminants (30,32,34) and possibly groundwater (58) from the soil. The invention further contemplates injection and extraction by means of recoverable extraction and injection probes (14) which obviate the need for permanent wells. The enhanced pressure gradient results from employing extraction in possible conjunction with injection at higher vacuum and pressure than previously known in the art.

BACKGROUND OF THE INVENTION 
1. Technical Field 
This invention relates generally to a system for decontaminating a 
contaminated volume of soil, and more particularly to an enhanced pressure 
gradient remediation system. 
2. Discussion 
Soil and groundwater purity has become an important environmental issue. 
Enormous amounts of contaminants now pollute numerous toxic sites. Spurred 
by federal legislation, a massive clean-up is underway. 
A contaminated volume of soil is generally characterized by trapped lenses 
of contaminants located above the water table level, at or near the water 
table level, or below the water table level. There may also be residual 
contamination of lower concentrations of contaminants trapped within the 
pores of the soil. Liquid contaminants which are heavier than water move 
downward into the capillary fringe in the water table while liquids 
lighter than water tend to spread laterally when they encounter the fringe 
of the water table. 
One method for cleaning up contaminated sites consists of removal of the 
contaminated soil. This method is bulky, impractical and slow. Another 
method is groundwater extraction to remove residual contamination. 
Groundwater withdrawal is intended to depress the water table in order to 
recover the spill, such as gasoline, in a separate phase. However, 
groundwater extraction is inefficient. However, the amount of free product 
typically recovered by this method is significantly less than the 
estimated amount of the spill. It cannot be predicted beforehand how much 
water must be pumped, for how long, or whether the pumping will be 
effective. Groundwater extraction may also require additional equipment 
such as down-hole pumps or entrainment tubes. 
Contaminated soil is typically decontaminated by installing at least one 
permanent extraction well connected to a vacuum pressure. This vacuum 
pressure is typically measured in terms of inches of water. This type of 
vacuum extraction is effective on volatile compounds, such as gasoline or 
solvents, and partially effective on semi-volatile compounds, such as 
diesel fuel. The effectiveness of a vacuum extraction system on 
semi-volatile compounds is on the order of 30%. Pure vacuum extraction 
only volatilizes compounds with particular vapor pressures, or Henry's 
constants. Typical in-situ vacuum extraction systems have limited success 
in finely-grained soils, require over 12 months of operating time and 
typically can only reduce concentrations of volatile contaminants in the 
soil to approximately 10 parts per million. 
Another technique is the injection of steam into the sub-surface to create 
a positive pressure gradient as well as increased sub-surface soil 
temperature to remove volatile and semi-volatile compounds. Steam enhanced 
extraction can remove other, less volatile compounds than vacuum 
extraction alone, but has not utilized high vacuum to forcibly assist the 
migration of sub-surface contaminants toward the extraction wells. The 
steam injection is also generally performed through permanent wells. 
As a result, existing technologies have required enormous capital 
expenditures for permanent wells, treatment of the entire contaminated 
area at the same time, and over 12 months of operating time. Permanent 
wells are more costly to install, more difficult and costly to abandon, 
and limit flexibility. 
SUMMARY OF THE INVENTION 
According to a preferred embodiment of the present invention, an enhanced 
pressure gradient system is disclosed incorporating at least one injection 
well by which steam is injected into a contaminated volume of soil, and at 
least one extraction well by which the steam, other fluids, and 
contaminants are extracted from the soil. The system employs a greater 
pressure gradient than is known in the art, resulting from high pressure 
injection and vacuum. The present invention may also be practiced by 
utilizing high vacuum independently or in conjunction with high pressure 
injection of ambient or heated air or stream, and may be coupled with 
groundwater extraction. The enhanced pressure gradient remediation 
increases the rate at which contaminants migrate towards the extraction 
wells, thereby decreasing the time required to complete remediation. 
Accordingly, it is an object of the present invention to provide an 
enhanced pressure gradient remediation system for effectively 
decontaminating a contaminated volume of soil. 
It is a further object of the present invention to provide a portable 
enhanced pressure gradient remediation system, utilization at least one 
probe removably drilled into the soil. 
Additional objects, advantages and features of the present invention will 
become apparent from the following description and appended claims, taken 
in conjunction with the accompanying drawings.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
The following description of the preferred embodiments is merely exemplary 
in nature and is in no way intended to limit the invention or its 
application or uses. 
According to a preferred embodiment of the present invention there is 
disclosed an enhanced pressure gradient remediation system for 
decontaminating a contaminated volume of soil. 
Referring to the drawings, FIG. 1 shows an enhanced gradient remediation 
system 10 according to a preferred embodiment of the present invention. 
The system 10 includes an injection well 12 for injecting pressurized 
fluid into the soil. The injection well 12 may be a conventional permanent 
well, or preferably a recoverable extraction and injection probe 14 which 
can be used for either injection or extraction of fluids. 
The injection probe 18 is constructed of an elongated hollow tube 26 having 
apertures 28 formed to allow flow of fluids in a generally horizontal 
direction. The apertures 28 are preferably located at levels below the 
depth of the contaminants 30,32 because the relatively hot steam will rise 
as it passes horizontally through the soil. The probe 18 further has a 
point 36 with auger flights 38 to allow the probe 18 to be removably 
drilled into the soil. 
The probe 18 is installed as follows. The point 36 is affixed to the lower 
end of a preferably five foot long tubular section. The upper end of the 
hollow tube 26 is affixed to a drive means 60 operative to rotate the 
probe 18 and drill it into the soil. The drive means 60 may be a 
conventional drill rig as is known in the art. The drive means 60 is 
utilized to drill successive tubular sections into the soil. The drive 
means 60 is removed from the hollow tube 26, and either a fluid injection 
system 16 or a fluid extraction system 44 is attached. Following 
remediation of the soil, the probe 18 is removed by a process in reverse 
of that disclosed above. 
A fluid injection system 16 is connected to the injection probe 18 by tubes 
20 and a coupling 22, and includes at least one steam boiler 24. The steam 
should preferably be injected at a pressure substantially within the range 
of 10 to 60 pounds per square inch, or 20 to 125 inches of mercury. Fluid 
injection pressures have previously been measured in terms of inches of 
water. The present invention thus contemplates much greater pressure than 
the prior art. If the injection medium is steam, it may also be injected 
below the surface of any groundwater. 
In an alternative embodiment, the fluid injection system 16 may be operated 
to inject ambient or heated air. 
The enhanced gradient remediation system 10 further includes an extraction 
probe 40 for extracting fluid and contaminants from the soil. The 
extraction may also be performed by a conventional permanent well. The 
extraction probe 40 is substantially similar to the injection probe 18, 
except that the extraction probe 40 is preferably formed with apertures 42 
more generally around the depth of the contaminants 30,32,34. 
A fluid extraction and treatment system 44 is connected to the extraction 
probe 40 by tubes 20 and a coupling 22. The extraction is preferably 
conducted by a vacuum substantially within the range of 5 to 30 inches of 
mercury. Again, this vacuum pressure is much higher than any known in the 
art. The enhanced pressure gradient results in faster remediation of the 
soil. In addition, the enhanced pressure gradient as well as the steam 
front washes or flushes the soil, remediating a greater variety of 
contaminants more effectively. 
Fluids and contaminants in the soil are drawn through the apertures 42 from 
the soil into the probe 40. Vacuum blowers 46 operating substantially 
within the range of 5 to 30 inches of mercury pull the extract through the 
probe 40, the coupling 22, and a liquid-vapor separator 48. The vapor is 
drawn by the vacuum blowers 46 into a vapor treatment system 50. The 
liquid proceeds through a separation tank 52, where water is removed and 
then treated by a treatment system 54. The remaining free product is 
stored and recycled 56. 
In an alternative embodiment, the extraction probe 40, fluid extraction 
system 44, and separation filters 48,52 and treatment systems 50,54,56 are 
operated independently, in the absence of any fluid injection 16. This 
embodiment may also correspond to operation of a combined injection and 
extraction system wherein the injection is temporarily halted. 
In another alternative embodiment, the extraction of fluid and contaminants 
from above the groundwater level is accompanied by groundwater extraction 
58. 
The proper selection of which embodiment to employ will depend upon various 
site-specific factors, such as groundwater level, depth and types of 
contaminants, and porosity of the soil. 
Enhanced gradient remediation is effective on volatile and semi-volatile 
compounds, even in finely-grained soils. The recoverable extraction and 
injection probes obviate the need for permanent wells. Utilization of 
probes makes the entire system portable, which permits remediation by a 
batch treatment approach and greatly reduces capital expenditures required 
for permanent technologies. 
The high pressure steam injection creates a steam front which forcibly 
washes or flushes the soil. As the steam passes through the soil, the 
contaminating substances 30,32,34 are carried conjunctively along with the 
steam in a substantially horizontal direction from the injection probe 18 
towards the extraction probe 40. The relatively hot steam will also rise 
as it passes through the soil. The high vacuum extraction of the 
extraction probe 40 acts to forcibly draw the injection fluid, preferably 
steam, and the contaminating substances 30,32,34 toward the extraction 
probe 40. 
As is apparent, an unlimited number of configurations of the probe can be 
realized and still satisfy the requirements described above. The foregoing 
discussion discloses and describes merely exemplary embodiments of the 
present invention. One skilled in the art will readily recognize from such 
discussion, and from the accompanying drawings and claims, that various 
changes, modifications and variations can be made therein without 
departing from the spirit and scope of the invention as defined in the 
following claims.