Method of removing volatile contaminants from contaminated earth strata

A method and apparatus of collecting volatile contaminants from a contaminated layer of earth. The apparatus is a closed-loop device which includes one or more contaminant withdrawal wells surrounded by multiple air reinjection wells connected by a conduit. One or more pumps serve to draw volatilized contaminant through the withdrawal well to the connecting conduit where it is captured or neutralized. Residual air from the withdrawal well is urged back into the ground through the air reinjection wells to encourage further contaminant to move toward the withdrawal well for collection.

FIELD OF THE INVENTION 
This invention relates to an improved method of removing volatile 
contaminants from permeable earth strata both above and below the water 
table and to apparatus for effecting the method which also captures or 
neutralizes the contaminants for effective disposal. 
BACKGROUND OF THE INVENTION 
Soil and water contamination due to spillage of volatile chemicals has long 
posed a serious problem in the obtainment of clean drinking and irrigation 
water. Initial studies in the contaminant removal area were conducted near 
landfill sites where migration of methane through the soil caused water 
and soil contamination in adjacent areas. The results of these studies may 
be found in various trade publications, referenced in my U.S. Pat. No. 
4,730,672, issued Mar. 15, 1988. 
There are several methods which have previously been used to remove 
industrial pollutants from contaminated earth strata both above the water 
table (vadose zone) and below the water table. The most common of these 
methods is excavation in which all of the contaminated soil is removed and 
eventually replaced with fresh earth. While excavation is a relatively 
simple process, it is not practical when large volumes are involved due to 
prohibitive cost and time factors. 
Another method involves a circulation system for leaching contaminants from 
the vadose layer into the water table where they are recovered by a water 
removal well and a pump. This process is shown generally in U.S. Pat. No. 
4,167,973 as well as other patents. Such processes are not always 
successful due to low water solubility of most common industrial 
pollutants, which results in lengthy and often costly recovery. 
A third method involves the creation of a vacuum within a withdrawal well 
in the vadose zone. By injecting air into the soil at points surrounding 
the withdrawal well, contaminants are urged towards the withdrawal well 
where they are vaporized and collected by vacuum withdrawal. Such method 
is described in U.S. Pat. No. 4,183,407 and 4,593,760. These methods are 
generally effective in contaminant recovery but do not provide for 
satisfactory disposal of most contaminants. 
SUMMARY OF THE INVENTION 
The method and apparatus of this invention utilizes the principles of 
vacuum vaporization and extraction of contaminants from the vadose layer. 
The method involves drilling one or more contaminant withdrawal wells into 
a layer of earth where contaminants are present. A plurality of air 
injection wells are drilled spaced from the central withdrawal well. 
Impermeable conduit is introduced into each well which is then backfilled. 
All conduits are connected for continued air flow and a neutralizing 
element placed between the withdrawal well conduit and the connecting 
conduits to provide clean air flow to all air injection wells and 
facilitate contaminant recovery. 
An equilibration chamber may also be connected to the contaminant recovery 
line and allows samples to be taken which confirm system efficiency during 
operation without the need for shutdown. It is understood that the 
withdrawal wells may be placed in any layer of permeable strata which 
contains contaminants, either above, in, or below the water table. 
Accordingly, it is an object of this invention to provide a novel method 
and apparatus for recovery of volatile contaminants from contaminated 
earth strata. 
Another object of this invention is to provide for a closed loop vacuum 
apparatus which efficiently draws vaporized contaminants from contaminated 
earth strata and which neutralizes the contaminants and recirculates clean 
air back to the earth. 
Another object of this invention is to provide for a soil contaminant 
recovery method which is economical. 
Still another object of this invention is to provide for a soil contaminant 
recovery method which complies with regulatory agency requirements and 
which allows quantitative testing to be performed during system operation 
to assure system efficiency. 
Other objects of this invention will be readily apparent upon a reading of 
the following description.

DESCRIPTION OF THE PREFERRED EMBODIMENTS 
The preferred methods and apparati herein described are not intended to be 
exhaustive or to limit the invention to the precise forms disclosed. They 
are chosen and described to explain the principles of the invention, and 
the application of the method to practical uses, so that others skilled in 
the art may practice the invention. 
The preferred method herein described may be best understood by following 
the description of the apparatus designated generally by the numeral 10 in 
the drawings. Apparatus 10 includes a withdrawal well 12 which is 
surrounded by a plurality of air injection wells 14 radially spaced from 
the withdrawal wells as seen in FIG. 2. Withdrawal well 12 is formed by 
establishing a borehole 16 into the vadose layer 18 of contaminated earth 
above the water table (not shown) with the borehole terminating above the 
water table. Vadose zone 18 may be of varying stratigraphic compositions, 
but for illustrative purposes is shown as including two layers 17, 19 of 
permeable stratum below surface 30, with an intermediate impermeable layer 
21 separating the two permeable layers. Loose pack fill 28, such as gravel 
is then poured into borehole 16 to a predetermined depth. Conduit, such as 
impermeable galvanized steel tubing 22 is positioned in borehole 16 spaced 
from the borehole outer wall just above fill material 28. Tubing 22 is 
open at its lower end 24 and at its upper end 26. Fluid permeable loose 
pack fill 28 is then backfilled into borehole 16 to a level just above 
tubing lower end 24 as determined by the individual site soil conditions. 
A quantity of impermeable fill 20 (such as bentonite or the like) is then 
packed about the remaining length of tubing 22 to the surface level 30, 
with the tubing upper end 26 extending slightly above the surface level. 
Each air injection well 14 is formed by establishing a borehole 32 in 
vadose layer 18 with the borehole terminating above the water table (not 
shown). Conduit, such as impermeable PVC tubing 34 is positioned in 
borehole 32 spaced from the borehole outer walls. Tubing 34 is open at its 
lower end 36 and at its upper end 38. A quantity of fluid permeable fill 
material such as loose pack gravel 40 is backfilled into borehole 32 to a 
level just above tubing lower end 36. A quantity of impermeable fill 39 
(such as bentonite or concrete) is then packed about the remaining length 
of tubing 34 to surface level 30 as shown in FIGS. 1 and 5. Boreholes 16, 
32 are shown as terminating in stratum layer 19, but it is understood that 
if contaminant is present in layer 17 that the boreholes may be drilled to 
allow contaminant withdrawal from this layer. Depth of wells 12, 14 will 
be dependent upon individual site stratigraphy and contaminant location 
and is not limited by this disclosure. 
It is understood that multiple withdrawal wells 12 may be formed to treat 
large volumes of contaminated earth. Multiple withdrawal wells 12 may also 
be used in smaller areas where the subsurface stratum configuration 
requires. Such techniques as placing of wells 12 and 14, as well as the 
appropriate depths of boreholes 16 and 32 are well within the realm of 
those skilled in the art. 
Conduit tubing 22 and 34 are preferably connected by a conduit 42 connected 
to the upper ends 26 and 38 of the respective tubing to form a closed loop 
circuit. Valves 44 may be positioned along conduit 42 adjacent tubing 
upper ends 26 and 38 to regulate air flow to and from conduits 22 and 34. 
Gauges 46 positioned adjacent valves 44 indicate the current air pressure 
level at the wellheads. 
Along conduit 42 between tubing ends 26 and 38 may be connected a variety 
of testing and filtering devices which are shown in FIG. 1. It is 
understood that these devices are not all necessary to the practice of the 
invention and elimination of one or more of them may be had and still 
maintain the spirit of this invention. The first such device is a 
conventional knock-out pot 49 which acts to encourage condensation of 
liquid water and/or contaminant from the air stream to maximize system 
efficiency. After passing through knock-out pot 49, the air stream passes 
through a solid particle filter 47 which screens out solid particles drawn 
up through conduit tubings 22 and 42 and which prevents mechanical damage 
to the vacuum source. The air stream then passes through a vacuum source 
48 which may be a vacuum pump (as shown), blower, exhaust fan or the like. 
Vacuum source 48 is oriented to drive the air stream in the direction 
indicated by arrows 50 of FIG. 1. Limit switches (not shown) may be 
included to shut down device 10 if conditions injurious to vacuum source 
48 should occur. A valve 52 and gauge 54 may be positioned along conduit 
42 to regulate and indicate air pressure at certain points along conduit 
42. 
After passing through vacuum source 48, the air stream may pass through 
exhaust muffler 56 and oil mist eliminator 58 which together act to 
capture any oil lost by the vacuum source, and also to collect water 
and/or contaminant for disposal through drain valves, respectively 60 and 
62. The air stream may then pass through heat exchange condenser 64 which 
may be cooled by non-contact water to enhance vapor condensation for 
collection through drain valve 66. One or more vacuum relief valves 68 may 
be positioned along conduit 42 as shown to prevent excessive load on the 
air injection pump 70. 
After passing through condenser 64, conduit 42 may be split into a high 
level contaminant monitor line 42a and a main flow contaminant line 42b. A 
quantitative monitor 72 is connected to and in fluid flow communication 
with high level contaminant line 42a and is utilized to measure 
contaminant vapor concentration within conduit 42. Limit switches (not 
shown) are connected to monitor 72 and serve to shut down device 10 if 
contaminant vapor concentration exceeds a predetermined value. 
Main flow contaminant line 42b may include an equilibration chamber 107 
(shown in detail in FIG. 7) in flow communication therewith through the 
flow conduit line 42d. Three valves 108, 109, 110 regulate flow through 
conduit 42d. A vacuum pump 112 acts in concert with valves 108-110 to draw 
vapor through line 42d and chamber 107. Chamber 107 preferably includes an 
inlet pipe 105 and an outlet 117 and is filled with fluid 114 such as 
water. Chamber 107 may also include a drain valve 116. To utilize chamber 
107, an operator opens valves 109-110 while closing valve 108 and drain 
valve 116 to allow the vapor flow from conduit 42b to pass into line 42d. 
The vapor enters chamber 107 through manifold pipe 119 which is below 
fluid 114. Any contaminant present in the vapor will begin to equilibrate 
with fluid 114 upon contact. When full equilibrium between fluid 114 and 
the vapor in chamber 107 is reached, valves 109-110 are closed, valve 108 
is opened and pump 112 is deactivated. A sample may then be taken through 
drain valve 16, after which chamber 107 is removed, drained, and refilled 
with additional fluid 114 if more equilibration testing is required. 
A condensate tank 74 is connected to and in fluid flow communication with 
main flow line 42b and may be equipped with a drain valve 76 for removal 
of condensate (oil, water and/or contaminant) and may include a limit 
switch to shut down device 10 if a preset limit is reached. 
The air stream next passes into a neutralizing member 88 which is in flow 
communication with line 42b. Neutralizing member may be an activated 
carbon bed which captures contaminant by adsorption, alternatively it may 
be a source of heat, catalysts, or other treatment members which allow 
neutralization or capture of the contaminant. After treatment in member 88 
the air stream passes into a contaminant sample line 42c connected to 
monitor 72 where it is analyzed for contaminant vapor concentration prior 
to delivery to air injection wells 14. Information concerning the 
contaminant is stored in a data logger 90 which may be accessed by a 
remote operator through telephone modem 92. 
The air stream then passes through injection compression source 70 which is 
preferably a blower or pump in communication with conduit 42 and which 
increases the pressure and volume to air injection wells 14 while reducing 
back pressure on vacuum source 48. Injection source 70 delivers the 
compressed air stream to a manifold 96 for distribution to air injection 
wells 14. Manifold 96 is illustrated in FIG. 2 and includes a single inlet 
98 and one or more outlets 100 which communicate with air injection wells 
14 through tubing 34. Valves 102 and gauges 104 accurately measure and 
regulate source pressure at each manifold outlet 100. The entire ground 
surface 30 is preferably covered by a fluid impermeable cover 106 of 
impervious vinyl or similar material to prevent percolation of air, water 
and contaminant through the surface during recovery operations. 
Device 10 is preferably operated as follows. With all components 
operatively connected, an operator switches on vacuum source 48 and air 
injection compression source 70. Vacuum source 48 creates an area of 
substantially reduced pressure in vadose layer 18 about withdrawal well 12 
to cause contaminants contained therein to vaporize and be drawn into 
conduit tubing 22, and through conduit 42 where the contaminant is 
eventually captured or neutralized by member 88. Any residual air drawn 
into the system is then charged from conduit 42 back into vadose layer 18 
through air injection wells 14 under pressure by compression source 70 to 
encourage migration of additional contaminants in the vadose layer to move 
toward withdrawal well 12 where they may be vaporized and collected for 
neutralization or capture. A continuous closed-loop process is the result. 
It should be noted that site stratigraphy will normally dictate the depths 
and configurations of withdrawal wells 12 and air injection wells 14. 
Several modifications of the device 10 may be possible depending upon site 
conditions and regulatory agency requirements. Two such modifications are 
shown in FIGS. 5 depicts an apparatus 10' in which air injection wells 14' 
are placed within the aquifer or water table 118. In this embodiment, air 
withdrawal wells 12' terminate in vadose zone 18 above water table 118. 
Clean air is injected through wells 14' into water table 118 creating 
bubbles and streams of air which rise through the water and around the 
soil particles. As the bubbles rise into vadose zone 18 they come into 
contact with liquid or vapor phase VOC's, which vaporize into the air 
bubbles and are carried to withdrawal wells 16' for removal. 
FIG. 6 depicts apparatus 10" in which air withdrawal wells 12" and air 
injection wells 14" terminate in a layer of high air of permeable stratum 
120 below water table 118 and separated by a layer of air impermeable or 
low permeability stratum 122. At the beginning, all wells 12", 14" are 
operated as air injection wells until a large air bubble is formed and 
detected at the normal air injection well 14". This air bubble forces 
water from the high permeability stratum 120 to create a sort of 
artificial vadose zone. Wells 12" and 14" are then operated as above 
described with the relative air volume injected and withdrawn monitored to 
maintain the dewatered condition within stratum layer 120. 
The scope of the invention is not to be considered limited by the above 
disclosure, and modifications are possible without departing from the 
spirit of the invention as evidenced by the following claims.