Title: Soil remediation of mercury contamination
Abstract: An in situ soil remediation system may be used to remove or reduce levels of mercury contamination within soil. The soil remediation system may also remove or reduce levels of other contaminants within the soil. Mercury may be vaporized within the soil by a heating system. The vaporized mercury may be removed from the soil by a vacuum system. The vaporized mercury may pass through heated risers that elevate the vaporized mercury. After the vaporized mercury passes from the heated risers, the vaporized mercury may be allowed to cool, condense, and flow downward to a treatment facility. Removing mercury from the soil as a vapor may provide an economical, safe, and efficient way to remediate mercury contaminated soil.
Patent Number: 6,962,466 Issued on 11/08/2005 to Vinegar, et al.
| Inventors:
|
Vinegar; Harold J. (Bellaire, TX);
Stegemeier; George L. (Houston, TX)
|
| Assignee:
|
Board of Regents, The University of Texas System (Austin, TX)
|
| Appl. No.:
|
279758 |
| Filed:
|
October 24, 2002 |
| Current U.S. Class: |
405/128.4; 405/128; 405/85 |
| Intern'l Class: |
B09C 001/00 |
| Field of Search: |
405/1281,128.15,128.2,128.25,128.3,128.35,128.4,128.6,128.7,128.8,128.85
|
References Cited [Referenced By]
U.S. Patent Documents
| 2777679 | Jan., 1957 | Ljunstrom.
| |
| 3684037 | Aug., 1972 | Bodine.
| |
| 4017309 | Apr., 1977 | Johnson.
| |
| 4276164 | Jun., 1981 | Martone et al.
| |
| 4380930 | Apr., 1983 | Podhrasky et al.
| |
| 4423323 | Dec., 1983 | Ellis et al.
| |
| 4500327 | Feb., 1985 | Nishino et al.
| |
| 4577503 | Mar., 1986 | Imaino et al.
| |
| 4598392 | Jul., 1986 | Pann.
| |
| 4641028 | Feb., 1987 | Taylor et al.
| |
| 4704514 | Nov., 1987 | Van Egmond et al.
| |
| 4842448 | Jun., 1989 | Koerner et al.
| |
| 4860544 | Aug., 1989 | Krieg et al.
| |
| 4974425 | Dec., 1990 | Krieg et al.
| |
| 4984594 | Jan., 1991 | Vinegar et al.
| |
| 5067852 | Nov., 1991 | Plunkett.
| |
| 5076727 | Dec., 1991 | Johnson et al.
| |
| 5114497 | May., 1992 | Johnson et al.
| |
| 5169263 | Dec., 1992 | Johnson et al.
| |
| 5190405 | Mar., 1993 | Vinegar et al.
| |
| 5193934 | Mar., 1993 | Johnson et al.
| |
| 5209604 | May., 1993 | Chou.
| |
| 5221827 | Jun., 1993 | Marsden, Jr. et al.
| |
| 5228804 | Jul., 1993 | Balch.
| |
| 5229583 | Jul., 1993 | van Egmond et al.
| |
| 5232951 | Aug., 1993 | Pfingstl et al.
| |
| 5233164 | Aug., 1993 | Dicks et al.
| |
| 5244310 | Sep., 1993 | Johnson.
| |
| 5249368 | Oct., 1993 | Bertino et al.
| |
| 5271693 | Dec., 1993 | Johnson et al.
| |
| 5305239 | Apr., 1994 | Kinra.
| |
| 5318116 | Jun., 1994 | Vinegar et al.
| |
| 5348422 | Sep., 1994 | Manchak, III et al.
| |
| 5360067 | Nov., 1994 | Meo, III.
| |
| 5362397 | Nov., 1994 | Cyr.
| |
| 5403119 | Apr., 1995 | Hoyle.
| |
| 5435666 | Jul., 1995 | Hassett et al.
| |
| 5545803 | Aug., 1996 | Heath et al.
| |
| 5553189 | Sep., 1996 | Stegemeier et al.
| |
| 5569154 | Oct., 1996 | Navetta.
| |
| 5656239 | Aug., 1997 | Stegemeier et al.
| |
| 5660500 | Aug., 1997 | Marsden et al.
| |
| 5674424 | Oct., 1997 | Iben et al.
| |
| 5753494 | May., 1998 | Hater et al.
| |
| 5779762 | Jul., 1998 | Kohr et al.
| |
| 5836718 | Nov., 1998 | Price.
| |
| 5997214 | Dec., 1999 | de Rouffignac et al.
| |
| 6039508 | Mar., 2000 | White.
| |
| 6102622 | Aug., 2000 | Vinegar et al.
| |
| 6419423 | Jul., 2002 | Vinegar et al.
| |
| 6543539 | Apr., 2003 | Vinegar et al.
| |
| 6632047 | Oct., 2003 | Vinegar et al.
| |
| 6688387 | Feb., 2004 | Wellington et al.
| |
| 2003/0110794 | Jun., 2003 | Stegemeier et al.
| |
| 2003/0136558 | Jul., 2003 | Wellington et al.
| |
| 2003/0192691 | Oct., 2003 | Vinegar et al.
| |
| 2004/0120772 | Jun., 2004 | Vinegar et al.
| |
| 2004/0126190 | Jul., 2004 | Stegemeier et al.
| |
| Foreign Patent Documents |
| 198 24 930 | Sep., 1992 | DE.
| |
| 196 48 928 | Apr., 1998 | DE.
| |
| 19707 096 | May., 1998 | DE.
| |
| 198 01 321 | Jul., 1999 | DE.
| |
| 199 27 134 | Dec., 2000 | DE.
| |
| 592 225 | Apr., 1994 | EP.
| |
| 1 366 357 | Sep., 1974 | GB.
| |
| 98/52704 | Nov., 1998 | WO.
| |
Other References
US Army Corps of Engineers Pamphlet EP 415-1-261, 1997, chapter 6.
U.S. Appl. No. 09/549,902 to Vinegar et al. entitled, "Vapor Collection and Treatment
of Off-Gas From an In-Situ Thermal Desorption Soil Remediation".
U.S. Appl. No. 10/279,771 to Stegemeier et al. entitled "Thermally Enhanced Soil
Decontamination Method".
U.S. Appl. No. 10/280,102 to Vinegar et al. entitled "Isolation of Soil With
a Low Temperature Barrier Prior to Conductive Thermal Treatment of the Soil".
Vinegar et al.; "In Situ Thermal Desorption of Soils Impacted with Chlorinated
Solvents"; 1999; 23 pgs.
Vinegar et al.; "In Situ Thermal Desorption using Thermal Wells and Blankets";
1998; 1 pg.
Conley et al.; "In Situ Thermal Desorption of Refined Petroleum Hydrocarbons
from Saturated Soil"; 2000; pp. 1-10.
Hansen et al.; "In Situ Thermal Desorption of Coal Tar"; 1998; pp. 1-22.
Vinegar et al.; "Remediation of Deep Soil Contamination using Thermal Vacuum
Wells"; Society of Petroleum Engineers; 1997; pp. 905-918.
Heron et al., "Soil Heating for Enhanced Remediation of Chlorinated Solvents:
A Laboratory Study on Resistive Heating and Vapor Extraction in a Silty, Low-Permeable
Soil Contaminated with Trichloroethylene"; Environmental science & Technology;
1998; 32(10); pp. 1474-1481.
International Search Report for PCT/US02/34199 mailed Jul. 2, 2003, 8 pages.
International Search Report for PCT /US02/34273 mailed Feb. 18, 2003, 3 pages.
International Search Report for PCT /US02/34532 mailed Aug. 5, 2003, 3 pages.
|
Primary Examiner: Kreck; John
Attorney, Agent or Firm: Meyertons, Hood, Kivlin, Kowert & Goetzel, P.C., Meyertons; Eric B.
Parent Case Text
PRIORITY CLAIM
This application claims priority to U.S. Provisional Application No. 60/336,325
entitled "Soil Remediation of Mercury Contamination," filed Oct. 24, 2001. The
above-referenced provisional application is hereby incorporated by reference as
if fully set forth herein.
Claims
1. A method of remediating mercury contaminated soil, comprising:
heating soil within a treatment area to vaporize mercury within the soil;
removing vaporized mercury and off-gas from the soil;
elevating the vaporized mercury and off-gas in a heated riser, wherein a portion
of the vaporized mercury is allowed to condense in the conduit and flow by gravity
to the treatment facility; and
transporting the vaporized mercury and off-gas to a treatment facility through
a conduit.
2. The method of claim 1, further comprising separating mercury from the off-gas
in the treatment facility.
3. The method of claim 2, further comprising treating the off-gas to reduce contamination
within the off-gas.
4. The method of claim 1, wherein the vaporized mercury is maintained in the
vapor state while passing through the conduit from the riser to the treatment facility.
5. The method of claim 1, wherein heating the soil comprises inserting heater
wells into the soil and heating the heater wells.
6. The method of claim 1, wherein heating the soil comprises using ground heaters
to heat the soil.
7. The method of claim 1, wherein removing vaporized mercury from the soil comprises
drawing mercury vapor from the soil into an extraction well coupled to the riser.
8. The method of claim 7, wherein the extraction well includes a heater element
configured to heat soil adjacent to the extraction well.
9. The method of claim 1, wherein removing vaporized mercury from the soil comprises
drawing a vacuum at ground surface through the riser.
10. The method of claim 1, further comprising monitoring mercury concentration
within the soil during remediation using a neutron logging tool.
11. The method of claim 1, further comprising injecting a drive fluid into the
soil within the treatment area, and producing a portion of the fluid from the soil.
12. The method of claim 1, further comprising forming a barrier around a portion
of a perimeter of the treatment area, extending the barrier to surround a second
treatment area, heating soil within the second treatment area, and removing vaporized
mercury and off-gas from the soil in the second treatment area.
13. The method of claim 12, wherein a portion of the barrier comprises a frozen barrier.
14. The method of claim 12, wherein a portion of the barrier comprises a grout wall.
15. The method of claim 12, wherein a portion of the barrier comprises a sheet pile.
16. The method of claim 12, further comprising heating less than all of the soil
of the treatment area adjacent to the second treatment area when heating soil within
the second treatment area, and removing off-gas from a portion of the treatment
area adjacent to the second treatment area simultaneously with removing vaporized
mercury and off-gas from the soil in the second treatment area.
17. A method for remediating mercury contaminated soil, comprising:
establishing a barrier around a portion of a perimeter of the contaminated soil;
placing a cover over the treatment area;
heating the soil within the treatment area;
removing off-gas from the soil through extraction wells;
elevating the off-gas in heated risers;
transporting the off-gas from the heated risers through conduits to a treatment
facility, wherein a portion of the mercury within the off-gas is allowed to condense
within the conduits and flow by gravity to the treatment facility.
18. The method of claim 17, further comprising drawing a vacuum at ground surface.
19. The method of claim 17, further comprising monitoring mercury concentration
within the soil during removal of off-gas from the soil using a neutron logging tool.
20. The method of claim 17, further comprising converting a ring of extraction
wells to injection wells, inserting a drive fluid into the soil through the injection
wells, and converting the ring of injection wells back to extraction wells.
21. The method of claim 17, wherein establishing the barrier comprises inserting
freeze wells into the ground and initiating the freeze wells to cool the soil to
freeze water within the soil and form a frozen barrier.
22. The method of claim 17, wherein establishing the barrier comprises inserting
metal sheet into the ground around the portion.
23. The method of claim 17, wherein establishing the barrier comprises forming
a grout wall in the ground around the portion.
24. The method of claim 17, wherein the cover comprises a metal sheet layer.
25. The method of claim 17, wherein the cover comprises a metal sheet layer and insulation.
26. The method of claim 17, wherein the cover comprises a metal sheet layer and
an impermeable layer.
27. The method of claim 17, wherein the cover comprises a metal sheet layer and
an impermeable layer, and wherein a vacuum is drawn between the metal sheet layer
and the impermeable layer.
28. The method of claim 17, further comprising extending the barrier to surround
a second treatment area, heating soil within the second treatment area, and removing
off-gas from the soil in the second treatment area.
29. The method of claim 28, further comprising heating less than all of the soil
of the treatment area adjacent to the second treatment area when heating soil within
the second treatment area, and removing off-gas from a portion of the treatment
area adjacent to the second treatment area simultaneously with removing off-gas
from the soil in the second treatment area.
30. The method of claim 17, wherein a portion of the conduits comprise flexible tubing.
31. The method of claim 17, wherein a portion of the conduits comprise plastic piping.
32. The method of claim 17, wherein the treatment facility comprises a carbon-sulfur
bed configured to react with mercury vapor.
33. The method of claim 17, wherein the treatment facility comprises a thermal oxidizer.
34. A method of remediating mercury contaminated with soil, comprising:
heating soil within a treatment area to vaporize mercury within the soil;
removing vaporized mercury and off-gas from the soil;
elevating the vaporized mercury and off-gas in a riser;
transporting the vaporized mercury and off-gas to a treatment facility through
a conduit;
forming a barrier around a portion of the treatment area;
extending the barrier to surround a second treatment area;
heating soil within the second treatment area to vaporize mercury within the
soil in the second treatment area; and
removing vaporized mercury and off-gas from the soil in the second treatment
area.
35. The method of claim 34, further comprising monitoring mercury concentration
within the soil during remediation using a neutron logging tool.
36. The method of claim 34, wherein a portion of the barrier comprises a frozen barrier.
37. The method of claim 34, wherein a portion of the barrier comprises a grout wall.
38. The method of claim 34, wherein a portion of the barrier comprises a sheet pile.
39. The method of claim 34, further comprising heating less than all of the soil
of the treatment area adjacent to the second treatment area when heating the soil
within the second treatment area, and removing off-gas from a portion of the treatment
area adjacent to the second treatment area simultaneously with removing vaporized
mercury and off-gas from the soil in the second treatment area.
40. A method for remediating mercury contaminated soil, comprising:
establishing a barrier around a portion of a perimeter of the contaminated soil;
placing a cover over the treatment area;
heating the soil within the treatment area;
removing off-gas from the soil through extraction wells;
transporting the off-gas from the extraction wells through conduits to a treatment
facility, wherein a portion of the mercury within the off-gas is allowed to condense
within the conduits and flow by gravity to the treatment facility;
extending the barrier to surround a second treatment area;
heating soil within the second treatment area; and
removing off-gas from the soil in the second treatment area.
41. The method of claim 40, wherein a portion of the vaporized mercury is allowed
to condense in the conduit and flow by gravity to the treatment center.
42. The method of claim 40, wherein the vaporized mercury is maintained in the
vapor state while passing through the conduit from the riser to the treatment facility.
43. The method of claim 40, further comprising monitoring mercury concentration
within the soil during removal of off-gas from the soil using a neutron logging tool.
44. The method of claim 40, wherein a portion of the barrier comprises a frozen barrier.
45. The method of claim 40, wherein a portion of the barrier comprises a grout wall.
46. The method of claim 40, wherein a portion of the barrier comprises a sheet pile.
47. The method of claim 40, further comprising converting a ring of extraction
wells to injection wells, inserting a drive fluid into the soil through the injection
wells, and converting the ring of injection wells back to extraction wells.
48. The method of claim 40, wherein the cover comprises a metal sheet layer and
an impermeable layer, and wherein a vacuum is drawn between the metal sheet layer
and the impermeable layer.
49. The method of claim 40, further comprising heating less than all of the soil
of the treatment area adjacent to the second treatment area when heating the soil
within the second treatment area, and removing off-gas from a portion of the treatment
area adjacent to the second treatment area simultaneously with removing off-gas
from the soil in the second treatment area.
50. The method of claim 40, further comprising heating less than all of the soil
of the treatment area adjacent to the second treatment area when heating soil within
the second treatment area, and removing off-gas from a portion of the treatment
area adjacent to the second treatment area simultaneously with removing vaporized
mercury and off-gas from the soil in the second treatment area.
51. A method of remediating mercury contaminated soil, comprising:
heating soil within a treatment area to vaporize mercury within the soil;
removing vaporized mercury and off-gas from the soil;
elevating the vaporized mercury and off-gas in a heated riser; and
transporting the vaporized mercury and off-gas to a treatment facility through
a conduit wherein a portion of the vaporized mercury is allowed to condense in
the conduit and flow by gravity to the treatment facility.
52. The method of claim 51, further comprising monitoring mercury concentration
within the soil during removal of off-gas from the soil using a neutron logging tool.
53. The method of claim 51, further comprising forming a barrier around a portion
of a perimeter of the treatment area, extending the barrier to surround a second
treatment area, heating soil within the second treatment area, and removing vaporized
mercury and off-gas from the soil in the second treatment area.
54. The method of claim 53, wherein a portion of the barrier comprises a frozen barrier.
55. The method of claim 53, wherein a portion of the barrier comprises a grout wall.
56. The method of claim 53, wherein a portion of the barrier comprises a sheet pile.
57. The method of claim 53, further comprising heating less than all of the soil
of the treatment area adjacent to the second treatment area when heating soil within
the second treatment area, and removing off-gas from a portion of the treatment
area adjacent to the second treatment area simultaneously with removing vaporized
mercury and off-gas from the soil in the second treatment area.
Description
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention generally relates to treatment of contaminated soil. An
embodiment of the invention relates to in situ thermal desorption soil remediation
of mercury contaminated soil.
2. Description of Related Art
Contamination of soil has become a matter of concern in many locations.
"Soil" refers to unconsolidated and consolidated material in the ground. Soil may
include natural formation material such as dirt, sand, and rock, as well as other
material, such as fill material. Soil may become contaminated with chemical, biological,
and/or radioactive contaminants. Contamination of soil may occur in a variety of
ways, such as material spillage, leakage from storage vessels, and landfill seepage.
Additional public health concerns arise if the contaminants migrate into aquifers
or into air. Soil contaminants may also migrate into the food supply through bioaccumulation
in various species in a food chain.
There are many methods to remediate contaminated soil. "Remediating soil" means
treating the soil to remove soil contaminants or to reduce contaminants within
the soil (e.g., to acceptable levels). A method of remediating a contaminated site
is to excavate the soil and to process the soil in a separate treatment facility
to eliminate or reduce contaminant levels within the soil. Many problems associated
with this method may limit its use and effectiveness. For example, dust generation
that accompanies excavation exposes the surrounding environment and workers to
the soil contamination. Also, many tons of soil may need to be excavated to effectively
treat even a small contamination site. Equipment, labor, transport, and treatment
costs may make the method prohibitively expensive compared to other soil remediation methods.
Biological treatment and in situ chemical treatment may also be used to
remediate soil. Biological and/or chemical treatment may involve injecting material
into the soil, such that the material reacts and/or moves contamination within
the soil. A material injected during a biological or chemical treatment may be
a reactant configured to react with the soil contamination to produce reaction
products that are not contaminated. Some of the reaction products may be volatile.
These reaction products may be removed from the soil.
The material injected during a chemical treatment may be a drive fluid configured
to drive the contamination toward an extraction well that removes the contaminant
from the soil. The drive fluid may be steam, carbon dioxide, or other fluid. Soil
heterogeneity and other factors may, however, inhibit uniform reduction of contaminant
levels in the soil using biological treatment and/or chemical treatment. Furthermore,
fluid injection may result in migration of contaminants into adjacent soil.
Soil vapor extraction (SVE) is a process that may be used to remove contaminants
from subsurface soil. During SVE, some vacuum is applied to draw air through the
subsurface soil. Vacuum may be applied at a soil/air interface or through vacuum
wells placed within the soil. The air may entrain and carry volatile contaminants
toward the vacuum source. Off-gas removed from the soil by the vacuum may include
contaminants that were within the soil. The off-gas may be transported to a treatment
facility. The off-gas removed from the soil may be processed in the treatment facility
to eliminate or reduce contaminants within the off-gas. SVE may allow contaminants
to be removed from soil without the need to move or significantly disturb the soil.
For example, SVE may be performed under roads, foundations, and other fixed structures.
Permeability of subsurface soil may limit the effectiveness of SVE.
Air and vapor may flow through subsurface soil primarily through high permeability
regions of the soil. The air and vapor may bypass low permeability regions of the
soil, allowing relatively large amounts of contaminants to remain in the soil.
Areas of high and low permeability may be characterized by, for example, moisture,
stratified soil layers, and fractures and material heterogeneities within the soil.
Water may be present within soil. At a certain level within some soil, pore
spaces within the soil become saturated with water. This level is referred to as
the saturation zone. In the vadose zone, above the saturation zone, pore spaces
within the soil are filled with water and gas. The interface between the vadose
zone and the saturated zone is referred to as the water table. The depth of the
water table refers to the depth of the saturated zone. The saturated zone may be
limited by an aquitard. An aquitard is a low permeability layer of soil that inhibits
migration of water.
Reduced air permeability due to water retention may inhibit contact of flowing
air with contaminants in the soil during SVE soil remediation. Dewatering the soil
may partially solve the problem of water retention. The soil may be dewatered by
lowering the water table and/or by using a vacuum dewatering technique. These methods
may not be effective methods of opening the pores of the soil to admit airflow.
Capillary forces may inhibit removal of water from the soil when the water table
is lowered. Lowering the water table may result in moist soil, which may limit
air conductivity.
A vacuum dewatering technique may have practical limitations. The vacuum generated
during a vacuum dewatering technique may diminish rapidly with distance from the
dewatering wells. The use of vacuum dewatering may not significantly decrease water
retention in the soil. This method may also result in the formation of preferential
passageways for air conductivity located adjacent to the dewatering wells.
Many types of soil are characterized by horizontal layering with alternating
layers of high and low permeability. A common example of a layered type of soil
is lacustrine sediments, characterized by thin beds of alternating silty and sandy
layers. Attempts to conduct SVE in such layers results in airflow that occurs substantially
within the sandy layers and bypasses the silty layers.
Heterogeneities may be present in soil. Air and vapor may preferentially
flow through certain regions or layers of heterogeneous soil, such as gravel beds.
Air and vapor may be impeded from flowing through other regions or layers of heterogeneous
soil, such as clay beds. Also, for example, air and vapor tend to flow preferentially
through voids in poorly compacted fill material. Air and vapor may be impeded from
flowing through overly compacted fill material. Buried debris within fill material
may also impede the flow of air through soil.
Some components of soil contamination may be toxic. Such soil contamination
may include mercury, mercury-containing compounds such as dimethyl mercury, radioactive
materials such as plutonium, volatile hazardous compounds, and combinations thereof.
Placement of wells or use of invasive testing procedures to identify the location
and extent of the soil contamination may require special measures to ensure that
the surrounding environment and workers are not exposed to contaminated vapor,
dust, or other forms of contamination during installation and use of the wells
or testing procedures. Such measures may include, but are not limited to, placing
dust or vapor producing operations within enclosures to prevent release of contaminants
to the environment, treating air within such enclosures to remove or reduce contamination
before releasing the air to the environment, equipping workers with appropriate
protective clothing, and/or equipping workers with appropriate breathing filters
or separate source air supplies.
In some cases, removal of some contaminants from affected soil may be impractical,
but removal of other contaminants may be desirable. For example, soil that is contaminated
with radioactive material may also be contaminated with other contaminants such
as mercury, mercury-containing compounds, hydrocarbons, and/or chlorinated hydrocarbons.
Removal of the radioactive material may be impossible or impractical, but it may
be desirable to remove or reduce other contaminants within the soil to inhibit
such contamination from migrating to other areas through the soil.
The presence of water within the ground is often a problem for construction projects.
The problem of water presence and/or water recharge may have to be overcome for
some construction projects. A barrier to water migration into a selected area may
be established by forming a freeze wall surrounding the selected area. The use
of freeze walls to stabilize soil adjacent to a work site and to inhibit water
migration into the work site has been implemented during construction of tunnels
and shafts and during excavation work. In a typical application of freeze wells
at a work site, freeze wells are inserted into the soil and a wall of frozen water
and soil is formed around a selected area. The soil within the selected area is
then excavated to form a hole. Supports may prevent the walls defining the hole
from falling in. The freeze wall may be allowed to thaw when sufficient support
is installed to prevent collapse of the walls. Alternatively, work within the hole
formed by the removal of the soil may be completed relying on the frozen wall of
water and soil to prevent the hole from collapsing. The frozen wall of water and
soil may be allowed to thaw after completion of the work within the well.
U.S. Pat. No. 2,777,679 issued to Ljungström, which is incorporated by
reference as if fully set forth herein, describes creating a frozen barrier to
define a perimeter of a zone that is to be subjected to hydrocarbon production.
Material within the zone is pyrolyzed by convectively advancing a heating front
through the material to drive pyrolysis products toward production wells. U.S.
Pat. No. 4,860,544, issued to Krieg et al., which is incorporated by reference
as if fully set forth herein, describes establishing a closed cryogenic barrier
confinement system about a predetermined volume extending downward from or beneath
a surface region of Earth, i.e., a containment site.
Mercury contamination in soil presents a serious long-term hazard. Instances
of widespread health problems resulting from mercury contamination have been documented
in many countries around the world. Some mercury contamination is due to spills
from industrial sources. For example, mercury spills from vessels that were used
as electrodes in chloro/alkali plants are known sources of mercury contamination.
Mercury contamination and mercury compound contamination may have occurred at mining
and ore processing sites, battery manufacturing facilities, and may also be due
to spills, leakage, and/or breakage of barometers, manometers, thermometers, mercury
switches, and other mercury containing instruments and vessels. Unacceptable levels
of mercury or mercury compounds may also be present in industrial and/or municipal sludge.
Elemental mercury may enter into soil if the pressure head of mercury exceeds
the capillary entry pressure of the soil. The mercury may continue to move downward
through the soil until the mercury encounters a low permeability layer in which
small pore sizes result in high capillary pressures that prevent entry of the mercury.
Mercury will typically pass into soil having a porosity greater than about 100
millidarcies. When the mercury reaches a barrier that it cannot pass into, the
mercury may flow laterally along the barrier and pool in low places. A portion
of a mercury spill that passes through soil may remain within pores of the soil.
The amount of mercury retained within the pores of the soil may depend on pore
shape and on mercury saturation. Typically, the pore space in a clean sandy soil
will hold from 5% to 20% by volume of residual mercury per pore volume of the soil.
The physical properties of mercury may make mercury hard to remove from soil.
The density of mercury (13.5 g/cc at 20° C.) may make it difficult to pump
mercury out of soil. The retention of a portion of mercury within soil pore space
may make it difficult to remove mercury from the soil so that the soil is no longer
considered to be contaminated by mercury. The low vapor pressure of mercury (e.g.,
0.0012 mmHg at 20° C. and 0.2729 mmHg at 100° C.) may make removal of
mercury by a soil vapor extraction process at low or slightly elevated temperatures
too time consuming to feasibly remediate mercury contaminated soil.
Mercury contaminated soil may be treated by soil excavation and subsequent
treatment of the soil to remove the mercury. Excavated soil may be treated by leaching
the mercury from the soil and/or by heating the soil to remove the mercury. Removal,
treatment, and transportation of mercury containing soil may not be practical for
large contaminated sites. Other types of soil contaminants, such as organic and/or
radioactive contaminants, may be present in mercury contaminated soil. Safety considerations
due to the presence of mercury and other types of contaminants may weigh against
the use of excavation and subsequent treatment of mercury contaminated soil as
a remediation method for treating the soil.
SUMMARY OF THE INVENTION
An in situ thermal desorption soil (ISTD) remediation system may be used to treat
mercury contaminated soil. The soil remediation system may be used to eliminate
or reduce to acceptable levels mercury, mercury compounds, and other removable
contaminants within the mercury contaminated soil. The mercury may be located in
an open location, or the mercury contamination may be located beneath a structure
such as a concrete slab of a building. If the contamination is located beneath
a structure, the structure may be moved, removed, or altered so that the heaters
and extraction wells of the soil remediation system contact the contaminated soil
beneath the structure.
Location, extent, and concentration of mercury contamination may be determined
prior to installing a soil remediation system that will remove or reduce to acceptable
levels contaminants within the soil. Non-intrusive tests may be used to establish
the location of mercury within the soil. The use of radar, gravimetric surveys,
and/or electromagnetic surveys may determine the presence of mercury within the
soil. The metallic characteristics of mercury may make large quantities of mercury
within the soil detectable using radar. The presence of water within the soil may
limit the effectiveness of radar as a mercury locating test. The presence of mercury
within soil may increase the average density of the soil. A measurable increase
in gravity may be indicated above soil that is contaminated with mercury. A gravity
survey may be used to detect density anomalies in the soil. A detected anomaly
may indicate the presence of mercury, or the detected anomaly may indicate the
presence of some other type of density anomaly in the soil. In addition to increasing
the average density of the soil, mercury may decrease the electrical resistance
of the soil and cause induced polarization. Radar indications, density anomalies,
decrease in soil resistance, and/or the presence of induced polarization may indicate
the presence of mercury contamination within an area of soil.
Non-intrusive testing, or substantially non-intrusive testing, such
as radar, gravimetric survey, or an electromagnetic survey may indicate the presence
of mercury within a region of soil. Such tests may indicate an area of mercury
contamination, but the tests may not give accurate concentration and depth information
of the contamination. After mercury contamination is found within the soil, the
extent, depth, and concentration of the mercury contamination may be determined
by intrusive tests. Test wells may be placed within the soil. Testing of cores
from the test wells and testing of fluid removed from soil through test wells may
be used to determine depth and concentration information of soil contamination.
A logging tool or tools may also be used to determine the mercury concentration
in situ. Logging tools may be important in determining the location, extent, and
concentration of mercury contamination prior to remediating the soil. Logging tools
may also be important in evaluating the progress and effectiveness of a soil remediation
process during the soil remediation. In an embodiment of a soil remediation system,
a neutron logging tool may be used to provide in situ measurements of mercury concentration.
A soil remediation system used to treat mercury contaminated soil may be an ISTD
soil remediation system. Heat may be applied to the soil by thermal blankets and/or
heater wells. The type of soil heater may be determined based on the depth of the
contaminants within the soil. Heater blankets may be used when contamination is
close to the ground surface. Heater wells may be used when the contamination is
deeper in the soil. The heat applied to the soil may raise the soil temperature
above the boiling point of mercury throughout a treatment area. A ring or rings
of heater-extraction wells may surround other remediation wells in a treatment
area. The heater-extraction wells may inhibit migration of contamination from the
treatment area during soil remediation.
Containment of mercury within the treatment area and reduction of airflow
throughout the treatment area may be enhanced by a ground cover and by a barrier
around a periphery of the treatment area. The barrier may inhibit migration of
soil contamination into adjacent areas. The barrier may also inhibit fluid flow
into the treatment area from adjacent areas. The barrier may be formed of sections
of steel plate or other type of material that are driven into the soil around the
periphery of the treatment area. Grouting, high temperature rubber seals, or other
types of seals may be used to couple individual sections together. Alternatively,
the barrier may be a frozen barrier formed by freeze wells placed around the periphery
of the treatment area.
A ground cover for a soil remediation system may inhibit release of vapor into
the air from a treatment area. The ground cover may also inhibit fluid from being
drawn into the soil from the ground surface. In an embodiment, the ground cover
may include a first steel sheet placed on the surface of the ground, a layer of
insulation on top of the first steel sheet, and a vapor barrier over the insulation.
Portions of wells extending into the soil may pass through the first steel sheet.
The wells may be welded or otherwise sealed to the barrier. The vapor barrier may
inhibit release of material that escapes past the first steel sheet and may also
inhibit air and/or water from being drawn into the soil from the surface. The vapor
barrier may be a steel barrier and/or a polymer barrier. The polymer barrier may
be, but is not limited to, polyethylene, polypropylene, silicone rubber, or combinations
thereof. The vapor barrier may be sloped to direct runoff rainwater to a desired
location. Condensate formed on an interior side of the vapor barrier may be gathered
and introduced into a treatment system of the soil remediation system to ensure
that any contaminants within the condensate are properly treated. A support structure
may be placed on top of the first steel sheet. The support structure may support
wells, risers, wiring, collection piping and other structures that pass into or
out of the ground within the treatment area.
A soil remediation system may include a perimeter barrier that surrounds or partially
surrounds a treatment area. The perimeter barrier may be a freeze wall, a grout
wall, and/or a number of sheets inserted into the ground to a desired depth and
sealed together. A seal may be formed between a portion of a ground cover and the
perimeter barrier. The seal may be, but is not limited to, a weld; adhesive; and/or
gaskets and clamping force provided by clamps, screws, bolts, or other types of
fasteners. The perimeter barrier may inhibit migration of contaminants out of the
treatment area. The perimeter barrier may also inhibit entry of fluid into the
treatment area from areas adjacent to the treatment area.
Off-gas removed from the treated soil may be maintained in a vapor state
within heated risers in the wells. Downstream from the riser, the mercury may condense
and flow downward through a surface conduit to a treatment facility. Alternatively,
the surface conduits may be heated to maintain contaminants in a vapor state in
route to the treatment facility. In embodiments where the conduit is not heater,
the conduit may be gas (e.g., air) or liquid cooled. The treatment facility may
include a separator to remove liquid mercury and other condensed liquids. The remaining
vapor may be passed through a treatment facility. The treatment facility may include
condensers, carbon beds, carbon sulfur beds, thermal oxidizers, and heat exchangers.
BRIEF DESCRIPTION OF THE DRAWINGS
Advantages of the invention will become apparent upon reading the following
detailed description and upon reference to the accompanying drawings in which:
FIG. 1 depicts a schematic representation of an embodiment of an in situ thermal
desorption (ISTD) soil remediation system.
FIG. 2 depicts a cross-sectional view of a portion of a soil remediation system.
FIG. 3 depicts a cross-sectional representation of an extraction well that includes
a heater element.
FIG. 4 depicts a plan view of a well pattern for a soil remediation system with
extraction wells, some of which do not include heater elements, and a double ring
of freeze wells.
FIG. 5 depicts a schematic diagram of a contamination treatment facility.
FIG. 6 depicts a plan view of well patterns for freeze wells and soil remediation
wells that may be used to treat a large contaminated area of soil.
While the invention is susceptible to various modifications and alternative
forms, specific embodiments thereof are shown by way of example in the drawings
and will herein be described in detail. The drawings may not be to scale. It should
be understood, however, that the drawings and detailed description thereto are
not intended to limit the invention to the particular form disclosed, but on the
contrary, the intention is to cover all modifications, equivalents, and alternatives
falling within the spirit and scope of the present invention as defined by the
appended claims.
DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS
An in situ thermal desorption (ISTD) process system may be used to remediate
contaminated
soil. An ISTD soil remediation process involves in situ heating of the soil to
raise the temperature of the soil while simultaneously removing off-gas by vacuum.
Heating the soil may result in removal of contaminants by a number of mechanisms.
Such mechanisms may include, but are not limited to: vaporization and vapor transport
of the contaminants from the soil; evaporation or entrainment and removal of contaminants
in an air or water vapor stream; and/or thermal degradation or conversion of contaminants
into non-contaminant compounds by pyrolysis, oxidation, or other chemical reactions
within the soil (e.g., contaminants other than mercury such as hydrocarbon and/or
chlorinated hydrocarbon contaminants).
An ISTD soil remediation process may offer significant advantages over soil vapor
extraction (SVE) processes and processes that depend on the injection of drive
fluids, chemical reactants, and/or biological reactants into the soil. Fluid flow
conductivity of an average soil may vary by a factor of 10
8 throughout
the soil due to differences in soil type (gravel, sand, clay) or to soil heterogeneities
and water within the soil. As used herein, "fluid" refers to matter that is in
a liquid or gaseous state. Mass transport of fluid through the soil may be a limiting
factor in the remediation of a treatment site using an SVE process or a chemical
and/or biological treatment of the soil. In contrast to the extremely large variation
in fluid flow permeability of soil, thermal conductivity of an average soil may
vary by a factor of only about two throughout the soil. Injecting heat into soil
may be significantly more effective than injecting a fluid through the same soil.
Furthermore, injecting heat into soil may also result in a preferential increase
in the permeability of the tight (low permeability) soil. Injected heat may dry
the soil. As the soil dries, microscopic and macroscopic permeability of the soil
may increase. The increase in permeability of heated soil may allow an ISTD soil
remediation process to remove or more uniformly reduce contaminants to acceptable
levels throughout a treatment area. The increase in soil permeability may allow
in situ remediation of low permeability clays and silts that are not amenable to
standard soil vapor extraction processes.
In a soil remediation embodiment, a method of decontamination includes heating
the contaminated soil to temperatures at which the contaminants are removed by
vaporization and/or thermal destruction. In situ water may vaporize and evaporate
or steam distill contaminants, allowing removal from the soil through extraction wells.
Soil may be heated by a variety of methods. Methods for heating soil include,
but are not limited to, heating by thermal radiation or conduction from a heat
source, heating by radio frequency heating, or heating by electrical soil resistivity
heating. "Radiative heating" refers to radiative heat transfer from a hot source
to a colder surface. "Conductive heating" refers to heat transfer by physical contact
of a media. Heat is transferred from a high temperature heater in a well to the
soil surface substantially by radiation. Heat is transferred primarily by conduction
from the heated soil surface to adjacent soil, thereby raising the soil temperature
at some distance from the heat source. Radiative and/or conductive heating may
be advantageous because temperatures obtainable by such heating are not limited
by the amount of water present in the soil. Soil temperatures substantially above
the boiling point of water may be obtained using thermal radiative and/or conductive
heating. Soil temperatures of about 100° C., 125° C., 150° C., 200°
C., 400° C., 500° C. or greater may be obtained using thermal radiative
and/or conductive heating. The heat source for radiative and/or conductive heating
may be, but is not limited to, an electrical resistance heater placed in a wellbore,
a heat transfer fluid circulated through a wellbore, or combustion within a wellbore.
Heaters may be placed in or on the soil to heat the soil. For soil contamination
within about 1 m of the soil surface, thermal blankets and/or ground heaters that
are placed on top of the soil may apply conductive heat to the soil. A vacuum system
may draw a vacuum on the soil through vacuum ports that pass through the thermal
blanket. The heaters may operate at about 870° C. U.S. Pat. No. 5,221,827
issued to Marsden et al., which is incorporated by reference as if fully set forth
herein, describes a thermal blanket soil remediation system. U.S. Pat. No. 4,984,594
issued to Vinegar et al., which is incorporated by reference as if fully set forth
herein, describes an in-situ method for removing contaminants from surface and
near-surface soil by imposing a vacuum on the soil beneath a impermeable flexible
sheet and then heating the soil with an electric surface heater that is positioned
on the soil surface under the sheet.
For deeper contamination, heater wells may be used to supply heat to the soil.
U.S. Pat. No. 5,318,116 to Vinegar et al; U.S. patent application Ser. No. 09/549,902
to Vinegar et al.; and U.S. Pat. No. 6,632,047 to Vinegar et al., each of which
is incorporated by reference as if fully set forth herein, describe ISTD soil remediation
processes for treating contaminated subsurface soil with thermal radiative or conductive
heating. U.S. Pat. No. 6,688,387 to Wellington et al.; U.S. Patent Publication
No. 20030136558 of Wellington et al.; and U.S. Patent Publication No. 20030192691
of Wellington et al. also describe heaters and various equipment. Each of these
applications is incorporated
