High vacuum extraction of soil contaminants along preferential flow paths

Abstract: Disclosed is a process for removing contaminants from a contaminated area (12) of the ground comprising soil having a first permeability, said ground having a plurality of paths (22,24,26) of preferential flow, each path having a permeability at least ten times greater than the first permeability, which process comprises providing a borehole (42) in the contaminated area to intersect at least a first path (22) of preferential flow and a second path (24) of preferential flow, said second path (24) of preferential flow being situated at a depth greater than said first path (22) of preferential flow; placing in the borehole (42) a first vacuum extraction pipe (30c) having a bottom opening situated within the first path (22) of preferential flow and a second vacuum extraction pipe (30) having a bottom opening situated within the second path (24) of preferential flow; isolating the first path (22) of preferential flow from the second path (24) of preferential flow so that a vacuum applied to the first vacuum extraction pipe (30c) with a bottom opening situated in the first path (22) of preferential flow will extract gases and liquids from the first path (22) of preferential flow but not from the second path (24) of preferential flow and a vacuum applied to the second vacuum extraction pipe (30b) with a bottom opening situated in the second path (24) of preferential flow will extract gases and liquids from the second path (24) of preferential flow but not from the first path (22) of preferential flow; applying a vacuum to at least one of the vacuum extraction pipes (30) to draw gases and liquid from at least one of the paths of preferential flow into a vacuum extraction pipe and transport both the gases and the liquid to the surface as a common stream; forming from the common stream a stream which is primarily liquid and a stream which is primarily gaseous; and removing contaminants from at least one of the liquid stream and the gaseous stream. Also disclosed is an apparatus for carrying out this process.

Description: The present invention is directed to processes for extracting contaminants from soil liquids and gases along paths of preferential flow in the ground. Although known apparatus and processes are suitable for their intended purposes, a need remains for processes and apparatus for removing contaminants from groundwater and soil which enables contaminant removal from soils of varying air permeability and varying porosity. Further there is a need for processes and apparatus for removing contaminants from groundwater and soil which enables increased flexibility in the location of extraction wells. There is also a need for processes and apparatus for removing contaminants from groundwater and soil that can be implemented by modifying existing vacuum extraction systems. Further, in some instances it may be desirable to remove contaminants from groundwater and soil gases from ground comprising relatively impermeable soils, such as silt, clay, mixtures of sand, silt, and clay, massive clay, or the like, or from ground comprising relatively impermeable rock, such as laminated sandstone, shale, mudstone, massive igneous and metamorphic rock, or the like. The permeability of these soils, which generally ranges from about 10 -6 to about 10 -8 centimeters per second or lower, is sufficiently low that many known processes for extracting ground contaminants are not suitable or efficient; known processes typically are suitable in soils with permeabilities of no less than about 10 -4 centimeters per second. Additionally, it may be desirable to remove contaminants selectively from one or more paths of preferential flow within an area of the ground, where areas of relatively low permeability are surrounded by areas of relatively high permeability. It is also desirable, in this instance, to be able to extract contaminants selectively from one or more paths of preferential flow through a single borehole or well. Extracting contaminants through a single borehole from multiple paths of preferential flow enables reduced installation costs, reduced and simpler apparatus, and less disruption to business in the contaminated area. Further, it may be desirable to apply vacuum extraction to one or more preferential flow paths while at the same time introducing a fluid (including gases and/or liquids) into one or more adjacent flow paths. In addition, it may be desirable to apply vacuum extraction to a plurality of preferential flow paths either simultaneously or in a desired sequence. US-A-3,251,413 describes the recovery of oil from oil-bearing formations having adjacent zones of uniform permeability. EP-A-498,676 describes the removal of contaminants from a ground area having a vadase zone and a water table. US-A-5,032,042 describes toxic contaminant treatment apparatus including a means for pneumatically fracturing the soil. EP-A-586,005 describes a process for removing contaminants from a contaminated area of the ground comprising: soil having a first permeability, said ground having a plurality of paths of preferential flow, each path having a permeability greater than the first permeability, which process comprises providing a borehole in the contaminated area to intersect at least a first path of preferential flow and a second path of preferential flow, said second path of preferential flow being situated at a depth greater than said first path of preferential flow; placing in the borehole a first vacuum extraction pipe, applying a vacuum to the vacuum extraction pipe to draw gases from at least one of the paths of preferential flow into a vacuum extraction pipe and transport the gases to the surface; forming a stream which is primarily liquid and a stream which is primarily gaseous; and removing contaminants from at least one of the liquid stream or the gaseous stream. The present invention provides the following features which are not described in EP-A-586,005: the vacuum extraction pipe has an opening situated within the first path of preferential flow; there is provided a second vacuum extraction pipe having a bottom opening situated within the second path of preferential flow; isolating the first path of preferential flow from the seocnd path of preferential flow so that a vacuum applied to the first vacuum extraction pipe with an opening situated in the first path of preferential flow will extract gases from the first path of preferential flow but not from the second path of preferential flow and a vacuum applied to the second vacuum extraction pipe with a bottom opening situated in the second path of preferential flow will extract gases from the second path of preferential flow but not from the first path of preferential flow; the difference in soil permeabilities is ten times; and liquids are withdrawn by vacuum with the gases, thereby, forming a common stream of gases and liquids. One object of the present invention is to provide a process and apparatus for removing contaminants from groundwater and soil with the above noted advantages. This and other objects of the present invention (or specific embodiments thereof) can be achieved by providing a process for removing contaminants from a contaminated area of the ground comprising soil having a first permeability, said ground having a plurality of paths of preferential flow, each path having a permeability at least ten times greater than the first permeability, which process comprises providing a borehole in the contaminated area to intersect at least a first path of preferential flow and a second path of preferential flow, said second path of preferential flow being situated at a depth greater than said first path of preferential flow; placing in the borehole a first vacuum extraction pipe having a bottom opening situated within the first path of preferential flow and a second vacuum extraction pipe having a bottom opening situated within the second path of preferential flow; isolating the first path of preferential flow from the second path of preferential flow so that a vacuum applied to the first vacuum extraction pipe with a bottom opening situated in the first path of preferential flow will extract gases and liquids from the first path of preferential flow but not from the second path of preferential flow and a vacuum applied to the second vacuum extraction pipe with a bottom opening situated in the second path of preferential flow will extract gases and liquids from the second path of preferential flow but not from the first path of preferential flow; applying a vacuum to at least one of the vacuum extraction pipes to draw gases and liquid from at least one of the paths of preferential flow into a vacuum extraction pipe and transport both the gases and the liquid to the surface as a common stream; forming from the common stream a stream which is primarily liquid and a stream which is primarily gaseous; and removing contaminants from at least one of the liquid stream and the gaseous stream. Another embodiment of the present invention is directed to an apparatus for removing contaminants from a contaminated area of the ground comprising soil having a first permeability, said ground having a plurality of paths of preferential flow, each path having a permeability at least ten times greater than the first permeability, said contaminated area of the ground being provided with a borehole extending downwardly from the surface of the ground to intersect at least a first path of preferential flow and a second path of preferential flow, said second path of preferential flow being situated at a depth greater than said first path of preferential flow, said apparatus comprising at least a first vacuum extraction pipe and a second vacuum extraction pipe situated inside of the borehole, wherein the first vacuum extraction pipe has a bottom opening situated within the first path of preferential flow and the second vacuum extraction pipe has a bottom opening situated within the second path of preferential flow, said first path of preferential flow being isolated from said second path of preferential flow so that a vacuum applied to the first vacuum extraction pipe with a bottom opening situated in the first path of preferential flow will extract gases and liquids from the first path of preferential flow but not from the second path of preferential flow and a vacuum applied to the second vacuum extraction pipe with a bottom opening situated in the second path of preferential flow will extract gases and liquids from the second path of preferential flow but not from the first path of preferential flow; a vacuum-forming apparatus in fluid communication with the first vacuum extraction pipe and the second vacuum extraction pipe and adapted to form a zone of reduced pressure in the first and second paths of preferential flow around the borehole, whereby gases and liquid can be drawn from the first and second paths of preferential flow into a vacuum extraction pipe and conveyed to the surface as a common stream; a vapor-liquid separator in fluid communication with said vacuum-forming apparatus and said first and second vacuum extraction pipes, wherein said vapor-liquid separator separates the common stream into separate gas and liquid streams; and a contaminant removal system, said contaminant removal system being situated to remove contaminants from at least one of the liquid stream and the gas stream. The present invention will be described further, by way of examples, with reference to the accompanying drawings, in which:- Illustrated schematically in Figure 1 is a side elevation view in cross section illustrating a general arrangement for vacuum extraction of contaminants from a contaminated area of the ground in accordance with the present invention. Illustrated schematically in Figure 2 is a cross-sectional view in side elevation of an extraction well suitable for the present invention. Illustrated schematically in Figure 3 is a cross-sectional view in side elevation of another extraction well suitable for the present invention. Illustrated schematically in Figure 4 is a cross-sectional view in side elevation of yet another extraction well suitable for the present invention. Illustrated schematically in Figures 5, 6, and 7 are cross-sectional views in side elevation of three suitable configurations for optional gas inlets into a vacuum extraction pipe in an extraction well of the present invention. Illustrated schematically in Figure 8 is a cross-sectional view in side elevation of an air inlet well suitable for use with the present invention. The present invention is directed to a process and apparatus for the removal of contaminants from groundwater and soil along paths of preferential flow. Contaminants can be present in the vadose zone and/or below the water table. Treated water can be returned to the soil or disposed of in conventional ways. In one embodiment of the invention, each vacuum extraction pipe is surrounded with a riser pipe. Each riser pipe is constructed with perforations (screening) which may be situated below the natural water table, in the unsaturated (vadose) zone, or both in the saturated and saturated zones. In one embodiment, one riser pipe has perforations both above and below the water table. In another embodiment of the invention, at least one riser pipe is constructed with perforations (screening) extending only below the water table. In yet another embodiment, at least one riser pipe has perforations only in the vadose zone above the water table. The unsaturated zone can be the natural vadose zone lying above the natural water table, or an expanded "artificial" vadose zone created when removal of the groundwater through the extraction well causes local lowering of the water table. Placing of the screening so that it extends both below the water table and into the vadose zone allows soil gases, including contaminants in the vapor phase, to be drawn into the riser pipe under the influence of a vacuum generator connected to the vacuum extraction pipe. The gases entrain the liquid phase, so that both phases can be transported to the surface together in a common stream through the vacuum extraction pipe. At the surface, the two phases are separated in a vapor-liquid disengaging vessel, such as a cyclone separator, knock-out pot or other suitable component, and after separation the phases can individually be routed to systems for contaminant removal by further treatment steps. Suitable processes for contaminant removal include filtration, adsorption, air stripping, settling, flocculation, precipitation, scrubbing and the like. As an alternative, one or more riser pipes can be situated so that the screening is at all times below the water table, even in the situation in which removal of water causes local depression of the water table. In such an arrangement, the fluid transported to the surface from this riser pipe is predominantly in the liquid phase, although it may still be necessary to provide vapor-liquid separation and individual phase treatment at the surface to deal with phase transformation which may occur as a result of turbulence and pressure reduction at the suction side of the vacuum device. A slotted riser pipe surrounding each vacuum extraction pipe is preferred when the soil is particulate to prevent the entrainment of silts, soils, or sediments into the vacuum extraction pipe, which could clog or damage the vacuum extraction system. When the surrounding soil is rock, slotted riser pipes are not necessary. Figure 1 (not drawn to scale) illustrates schematically a system, designated generally by the reference numeral 10, for vacuum extraction and treatment in accordance with the invention. Seen in Figure 1 is a contaminated zone 12, wherein the contaminants in central zone 14 are more highly concentrated in the soil than in surrounding zone 12. The contaminants are adsorbed, dissolved, or suspended free phase and gaseous phase contaminants in the soil. As illustrated in Figure 1, dashed line 16 represents the interface between upper soil 18, which typically is more permeable than lower soil 20. For example, upper soil 18 may be weathered clay, with a typical permeability of about 1 × 10 -7 centimeters per second, and lower soil 20 may be unweathered clay, with a typical permeability of about 1 × 10 -8 centimeters per second. It is not required, however, for the purposes of the present invention, that contaminated zone 12 extend into two or more areas of differing soil permeability; contaminated zones 12 and 14, preferential flow paths 22, 24, and 26, and extraction well 28 may all be situated within soil of a single permeability. Within the soil containing contaminated zone 12 are paths of preferential flow 22, 24, and 26, wherein the soil is significantly more permeable than either upper soil 18 or lower soil 20. The permeabilities of soil within the preferential flow paths typically are at least one order of magnitude greater than the permeability of the soil surrounding the preferential flow paths. For example, the surrounding soil might have a permeability of about 1 × 10 -4 centimeters per second or less while the paths of preferential flow might have permeabilities of 1 × 10 -3 centimeters per second or greater. These paths of preferential flow may be either naturally occurring or may be artificially created in the contaminated area. Artificial preferential flow paths can be created by, for example, fracturing processes, wherein relatively permeable flow areas are created within relatively impermeable soil. For example, hydraulic fracturing entails driving a casing and a lance tip, said casing and lance tip being of any suitable material, such as steel or the like, into the soil to the desired depth of the fracture closest to the surface. Thereafter, an extension rod is driven into the casing to drive the lance tip further into the soil, to a depth below the terminal end of the casing. The extension rod and lance tip are thereafter removed from the casing, leaving the empty casing in the ground with a well of exposed soil below the terminal end of the casing. A notch is then cut in the soil below the terminal end of the casing by a cutting jet of water, said notch extending horizontally and perpendicular to the vertical casing. Thereafter, a sand-filled slurry is injected under pressure into the casing; the casing prevents diffusion of the slurry in all areas except the exposed soil within the notch below the terminal end of the casing, and the pressure causes a horizontal hydraulic fracture to be extended from the notch edges. The fracture thus created contains sand, which assists in prevention of future collapse of the fracture, and enables gases and liquids to flow through the fracture at rates significantly higher than are possible in the relatively impermeable surrounding soil. Thereafter, additional fractures can be created at progressively lower levels by inserting a longer casing and the lance tip into the original hole in the ground and driving them to the desired depth, followed by cutting of a new notch at a lower level and injection of the slurry to create a new fracture. Fractures can be created at any desired spacings, typically at least 6 inches (15 centimeters) apart, although the distance between fractures may be lower if desired. In a preferred embodiment, the slurry injected into the fractures comprises a mixture of sand, water, and crosslinked guar gum, the mixture being highly viscous. The mixture also includes a chemical agent such as an enzyme that attacks the crosslinking in the guar gum, so that over a period of time, typically about 1 or 2 days, the crosslinking in the guar gum breaks down, thereby lowering the viscosity of the slurry. Thereafter, the water drains from the slurry, leaving the sand remaining in the fracture. One example of a suitable commercially available additive to a sand/water slurry for this purpose is the REVERT® drilling fluid additive, available from Johnson Filtration Systems, Inc., St. Paul, MN. This material contains guar gum and initially enhances the viscosity of the slurry, followed by a breakdown of the guar gum and resulting decreased viscosity within a few days. Optionally, air inlet probes 27 may be provided within one or more of preferential flow paths 22, 24, and 26. The air inlet probes allow air or other fluids (liquids and/or gases) to be introduced into the preferential flow paths at a location spaced from the well, said fluids then being extracted through the well bore. This arrangement may be beneficial in situations where insufficient communication otherwise exists between the atmosphere and the extraction well or if the soil is incapable of yielding sufficient air flow. An extraction well 28, which will be described in greater detail shortly, is sunk in the area of the contaminated zone 12 and extends through the upper soil 18 and into the lower soil 20. Associated with the extraction well 28 is a vacuum extraction system, designated by the reference numeral 32, preferably designed to generate high vacuum conditions, typically from about 2.3×10 4 to 9.8×10 4 Pa (7 to about 29 inches of mercury). Gases removed by the vacuum extraction system 32 can be vented to atmosphere at 34 if within acceptable environmental limits, or further processed, such as by being incinerated or passed to a condenser, granular activated carbon filter, or other such component 36. The component 36 serves to remove contaminants from the extracted gases. Water extracted by the process can be treated by passing it through conventional systems for metals removal, volatile organic compound removal, or other steps of purification. The treated and purified water, if it is of sufficient purity at this stage, can be returned to a sewer or directly to the ground as indicated at 38. Contaminants can be stored in drums 40 for eventual destruction or further processing. Figures 2, 3, and 4 (not drawn to scale) illustrate embodiments of extraction well 28 in greater detail. As illustrated schematically in Figures 2, 3, and 4, the extraction well 28 in the illustrated form of the invention includes an elongated borehole 42, into which are placed perforated riser pipes 44a, 44b, and 44c, each capped at the bottom. The riser pipes 44a, 44b, and 44c are perforated either above the water table, below the water table or both below and above the water table. In the embodiment illustrated, the riser pipes include an imperforate upper portion 46a, 46b, and 46c and a perforate (screened) lower portion 48a, 48b, and 48c. The riser pipes 44a, 44b, and 44c can be of any suitable material, such as polyvinyl chloride, metals, such as stainless steel, galvanized steel, or the like, plastics, including Teflon®, or the like. The screened or perforate portions can have perforations of any desired or suitable shape and size; for example, in one embodiment, the perforated portion can be equipped with 0.25 mm (0.010 inch) slots. Situated inside riser pipes 44a, 44b, and 44c are vacuum extraction pipes 30a, 30b, and 30c. The vacuum extraction pipes 30a, 30b, and 30c can be of any suitable material, such as polyvinyl chloride, metals, such as stainless steel, galvanized steel, or the like, plastics, including Teflon®, or the like. The upper ends of the riser pipes 44a, 44b, and 44c are here shown to be associated with a concrete floor or deck, and are provided with suitable pipe fittings 52, enabling the riser pipes 44a, 44b, and 44c and the vacuum extraction pipes 30a, 30b, and 30c to be coupled to the remainder of the vacuum extraction system 32 (not seen in Figures 2, 3, and 4), with vacuum extraction pipes 30a, 30b, and 30c being in fluid communication with the vacuum extraction system. Preferably, vacuum extraction pipes 30a, 30b, and 30c are capable of operating independently of one another. Thus, in one embodiment, vacuum is applied simultaneously to vacuum extraction pipes 30a, 30b, and 30c. In another embodiment, vacuum is applied sequentially to the pipes with, for example, vacuum being first applied only to pipe 30a, followed by application of vacuum to pipe 30b, either with or without continued application to pipe 30a, and then followed by application of vacuum to pipe 30c, either with or without continued application to pipes 30a and/or 30b. In yet another embodiment, vacuum is applied to one vacuum extraction pipe, such as 30a, for example, while a gas is introduced into another extraction pipe with an opening situated deeper in the ground than the pipe to which vacuum is applied, such as 30c for example. In still another embodiment, vacuum is applied to one vacuum extraction pipe, such as 30c, for example, while a gas is introduced into another extraction pipe with an opening situated at a shallower level in the ground than the pipe to which vacuum is applied, such as 30a for example. Any other combination of application of vacuum, positive pressure, or neither to the plurality of pipes in the well is also possible. Vacuum extraction pipes 30a, 30b, and 30c all have bottom openings within extraction well 28. Each vacuum extraction pipe is situated so that its bottom opening is within a preferential flow path. For example, as shown in Figure 2, vacuum extraction pipe 30a is situated within preferential flow path 26, vacuum extraction pipe 30b is situated within preferential flow path 24, and vacuum extraction pipe 30c is situated within preferential flow path 22. The preferential flow paths 22, 24, and 26 and the bottom openings of vacuum extraction pipes 30a, 30b, and 30c are isolated from each other by layers of relatively impermeable soil or rock and, within the borehole, by essentially impermeable seals surrounding the impermeable portions 46a, 46b, and 46c of riser pipes 44a, 44b, and 44c. For example, as illustrated in Figure 2, the bottom opening of vacuum extraction pipe 30c is isolated within preferential flow path 22 by grout layers 54a and 54b and by bentonite cement layers 56a and 56b. The bottom opening of vacuum extraction pipe 30b is isolated within preferential flow path 24 by grout layers 54b and 54c and by bentonite cement layers 56b and 56c. The bottom opening of vacuum extraction pipe 30a is isolated within preferential flow path 26 by grout layer 54c and bentonite cement layer 56c and by the bottom of borehole 42. Sand 49 situated within the borehole 42 supports the bentonite cement and grout layers within the borehole and riser pipe. Any other suitable or desired materials can also be employed for isolating the preferential flow paths from each other, such as other grouts, bentonite clays, nonshrink epoxy materials, hydraulic cements, plastics, rubber materials, or the like. While not necessary, it is preferred that the bottoms of vacuum extraction pipes 30a, 30b, and 30c terminate at an angle other than exact parallel with the horizontal; by terminating the pipe at an angle, the surface area of the opening is increased, which enhances the ease of starting the well. Preferred angles for the bottom opening of vacuum extraction pipes 30a, 30b, and 30c are from about 10° to about 80° with respect to the horizontal, and more preferably about 45° with respect to the horizontal, although the angulation can be outside this range. In one embodiment of the present invention, situated at the end of extraction well 28 at or near the ground surface are one or more optional air inlets 31 associated with at least one riser pipe, said optional inlet 31 preferably being equipped with an air flow gauge (not shown), which permits the introduction of air at any desired pressure, including reduced pressures, atmospheric pressure, or increased or forced pressures, into riser pipes 44a, 44b, and/or 44c; preferably, separate connections enable introduction of air selectively into at least one but not others of 44a, 44b, and 44c. As shown, inlet 31a permits introduction of air into riser pipe 44a, inlet 31b permits introduction of air into riser pipe 44b, and inlet 31c permits introduction of air into riser pipe 44c. When it is desired to add air at pressures greater than atmospheric pressure, air pressure can be provided by an additional pump (not shown), by connecting the outlet or exhaust of the vacuum pump connected to vacuum extraction pipes 30a, 30b, and/or 30c to an air inlet, or the like. The air flow rate through an air inlet can range from nearly zero to any value less than the m 3 /s (CFM) rated capacity of the vacuum pump connected to vacuum extraction pipes 30a, 30b, and 30c. While some air flow may be desirable at system start-up, after the process has been in operation for a period of time, the air flow may in some instances be reduced to zero, with no air being introduced into the well through the air inlet or inlets and maximum vacuum being applied to the sub-surface soil and water. In addition, the air introduced through the air inlet or inlets can, if desired, be heated to improve the extraction of some contaminants. Further, the air inlet or inlets can be used as an inlet for introducing other materials or chemicals into the riser pipe and extraction stream, since chemicals or materials so introduced will pass down with the inlet air through the riser pipe to the bottom thereof, and then back up with the water and air mixture through vacuum extraction pipe 30, thus chemically or otherwise interacting with the water and air mixture. For example, oxidizers or surfactants or other chemicals can be introduced for the treatment of water-borne or vapor-borne contaminants removed by the vacuum extraction pipe. Additionally, in situations wherein the apparatus and process of the present invention are employed in conjunction with a biotransformation process, wherein soil contaminants are biologically transformed into innocuous materials by interaction with bacteria or other biological methods, gas inlet or inlets can be employed to introduce into the vacuum extraction pipe nutrients for biotransformation, such as cellulose or the like, or for introducing nitrogen to enhance anaerobic processes or oxygen to enhance aerobic processes. These materials can also be added through one or more of the vacuum extraction pipes 30a, 30b, or 30c or through one or more of the air inlet probes 27. Further information regarding biological processes for treating soil contaminants is disclosed in, for example, W. K. Ahlert et al., "In situ Bioremediation of Soil Contaminated with Methyl Benzene Species," M. A. Franson, "In Situ Bioremediation of Unleaded Gasoline Contaminated Ground Water, Plainfield, Connecticut, A Case Study," and M. Leavitt et al., "Implications of Surfactant Augmentation for In Situ Bioremediation Systems," all contained in In Situ Treatment of Contaminated Soil and Water, Proceedings of the 1992 U.S. EPA/A&WMA International Symposium, Air and Waste Management Association (Pittsburgh 1992); and Subsurface Restoration Conference, June 21 - 24, 1992, Dallas, Texas (Rice University Dept. of Envi. Sci. & Eng., Houston TX 1992). Liquid drawn up through vacuum extraction pipes 30a, 30b, and 30c preferably, although not necessarily, is in two-phase form, namely droplets, mist, and/or vapor entrained in liquid, as opposed to slug flow. Air flow through the system is provided by one or more of the following: air from the unsaturated (vadose) zone; air from the dewatered saturated zone; air from one or more of the optional air inlet mechanisms 31, at reduced pressures, atmospheric pressure, or forced pressures; air from optional gas inlet or inlets 41 at atmospheric pressure or forced pressures; and air introduced through one preferential flow path (through either an air inlet probe 27 or through a vacuum extraction pipe 30) and extracted from another preferential flow path. Thus, it is not required that air be extracted from the ground in the vicinity of the extraction well. Generally, a high vapor/air velocity is maintained through the system. Air velocity in the vacuum extraction pipe should be sufficient to carry or lift water in the vapor phase, either droplets of various sizes, or the like, entrained in the air. Air velocity values in the range of from about 0.3 m/s to about 61 m/s (1 foot per second to about 200 feet per second) or greater generally suffice. Vacuum extraction pipes 30a, 30b, and/or 30c each can optionally be equipped with at least one gas inlet 41. As illustrated in Figure 2, vacuum extraction pipe 30c is equipped with a single optional gas inlet 41. As illustrated schematically in Figure 3, in which, for the sake of simplicity, only a single vacuum extraction pipe 30 is shown (although in actual operation at least two riser pipes containing vacuum extraction pipes would be situated in borehole 42), the vacuum extraction pipe 30 is equipped with three optional gas inlet tubes 41a, 41b, and 41c. As illustrated schematically in Figure 4, vacuum extraction pipe 30 is equipped with three optional gas inlets 41d, 41e, and 41f, all feeding from a single gas inlet tube 41. More specifically, as shown in Figure 2, optional gas inlet 41 enters vacuum extraction pipe 30 from the bottom opening of vacuum extraction pipe 30. Alternatively (not shown), gas inlet 41 can enter vacuum extraction pipe 30 through an opening in the side of vacuum extraction pipe 30. Gas inlet 41 is in fluid communication with a gas supply, which can be either atmospheric air or some other desired gas, and with optional air compressor 43. A tank containing compressed air can also serve as the gas supply. The gas supply to gas inlet 41 is controlled through valve 45 and the pressure in gas inlet 41, if desired, can be monitored with optional pressure gauge 47. In addition, if desired, an automatic controller for turning valve 45 on and off and/or for controlling the duration and/or pressure of the gas applied to vacuum extraction pipe 30 from gas inlet 41 can be added to the configuration of gas inlet 41. As shown in Figure 3, optional gas inlets 41a, 41b, and 41c enter vacuum extraction pipe 30 through openings in the sides of vacuum extraction pipe 30. Gas inlet 41b can be situated above, at, near, or below the level of the water table (and correspondingly above, at, near, or below the approximate level of groundwater which has entered vacuum extraction pipe 30 prior to initiation of the pumping process). Gas inlet 41a is generally situated at a level below the natural water table but above the level to which the groundwater drops after the pumping process has been in operation for a period of time. Gas inlet 41c is situated at a level below the level to which the groundwater drops after the pumping process has been in operation for a period of time. While gas inlet 41c is shown in this illustration as entering vacuum extraction pipe 30 through an opening in the side wall of vacuum extraction pipe 30 immediately above the bottom opening of vacuum extraction pipe 30, gas inlet 41c may also enter vacuum extraction pipe 30 either directly through the bottom opening of vacuum extraction pipe 30 or through either side of vacuum extraction pipe 30. The number of optional gas inlets in this embodiment of the invention is not limited to two or three; for example, in a well 200 feet deep, a greater number of gas inlets may be desired. In addition, the optional gas inlet openings into vacuum extraction pipe 30 need not be evenly spaced with respect to each other; the length of each gas inlet may vary as desired for optimal operation of the well. Gas inlets 41a, 41b, and 41c are each in fluid communication with gas supplies, which can be either atmospheric air or some other desired gas, and with optional air compressors 43a, 43b, and 43c. Tanks containing compressed air can also serve as the gas supplies. The gas supplies to gas inlets 41a, 41b, and 41c are each controlled through valves 45a, 45b, and 45c, and the pressures in gas inlets 41a, 41b, and 41c, if desired, can be monitored with optional pressure gauges 47a, 47b, and 47c. In addition, if desired, an automatic controller for turning valves 45a, 45b, and 45c on and off and/or for controlling the duration and/or pressure of the gas applied to vacuum extraction pipe 30 from gas inlets 41a, 41b, and 41c can be added to the configuration of gas inlets 41a, 41b, and 41c. As shown in Figure 4, in which, for the sake of simplicity, only a single vacuum extraction pipe 30 is shown (although in actual operation at least two vacuum extraction pipes would be situated in borehole 42), optional gas inlets 41d, 41e, and 41f enter vacuum extraction pipe 30 through openings in vacuum extraction pipe 30. Gas inlets 41d, 41e, and 41f are all in fluid communication with main gas inlet 41. The diameter of gas inlet 41d, situated closest to the top of vacuum extraction pipe 30, is smaller than the diameter of gas inlet 41e situated between gas inlets 41d and 41f. The diameter of gas inlet 41e is smaller than the diameter of gas inlet 41f situated closest to the bottom opening of vacuum extraction pipe 30. Gas inlet 41d can be situated above, at, near, or below the level of the water table (and also correspondingly above, at, near, or below the approximate level of groundwater which has entered vacuum extraction pipe 30 prior to initiation of the pumping process). Gas inlet 41e is generally situated at a level below the natural water table but above the level to which the groundwater drops after the pumping process has been in operation for a period of time. Gas inlet 41f is situated at a level below the the level to which the groundwater drops after the pumping process has been in operation for a period of time. While gas inlet 41f is shown in this illustration as entering vacuum extraction pipe 30 through an opening in the side wall of vacuum extraction pipe 30 immediately above the bottom opening of vacuum extraction pipe 30, gas inlet 41f may also enter vacuum extraction pipe 30 either directly through the bottom opening of vacuum extraction pipe 30 or through either side of vacuum extraction pipe 30. The number of optional gas inlets in this embodiment of the invention is not limited to two or three; for example, in a well 200 feet deep, a greater number of gas inlets may be desired. In addition, the optional gas inlet openings into vacuum extraction pipe 30 need not be evenly spaced with respect to each other; the distances between gas inlets may vary as desired for optimal operation of the well. The gas supply to gas inlet 41 is controlled through valve 45 and the pressure in gas inlet 41, if desired, can be monitored with optional pressure gauge 47. In addition, if desired, an automatic controller for turning valve 45 on and off and/or for controlling the duration and/or pressure of the gas applied to vacuum extraction pipe 30 from gas inlet 41 can be added to the configuration of gas inlet 41. The relative diameters of gas inlet openings 41d, 41e, and 41f are selected so that when compressed air is applied to gas inlet 41, the compressed air will preferentially be directed first to 41d, followed by 41e, and then followed by 41f, thus resulting in the top, middle, and bottom sections of the vacuum extraction pipe being started in sequence. The opening of smallest diameter, 41d, is situated at the top and the opening of largest diameter, 41f, is situated at the bottom because more compressed air is needed to overcome the effect of the head due to the depth of the well and the length of the extraction tube needed to start the system. In operation, gas is introduced into vacuum extraction pipe 30 either before, while, or after a vacuum is applied to vacuum extraction pipe 30 to initiate two-phase flow within vacuum extraction pipe 30. In the embodiment wherein vacuum extraction pipe 30 is equipped with a single gas inlet 41 as illustrated in Figure 2, gas is applied through gas inlet 41 continuously as vacuum is applied to vacuum extraction pipe 30 until two-phase flow is established within vacuum extraction pipe 30, at which point the flow of gas through gas inlet 41 is halted. The actual duration for application of gas through gas inlet 41 will vary depending on factors such as the depth of the well, the depth within the well of the gas inlet 41, the depth of groundwater contained within vacuum extraction pipe 30, the dimensions of the well, vacuum extraction pipe 30, and gas inlet 41, the pressure of gas applied through gas inlet 41, and the like. Typical duration times for wells 4 inches in diameter and wherein gas is introduced at a pressure of from about 20 to about 60 pounds per square inch are from about 15 to about 20 seconds when the groundwater level is less than 15 feet deep and about 45 seconds when the groundwater level is from about 18 to about 25 feet deep. In some instances, durations for applying gas through gas inlet 41 may be 5 minutes or greater. In embodiments of the present invention wherein vacuum extraction pipes 30a, 30b, and/or 30c are equipped with a multiplicity of gas inlets, as illustrated in Figure 3 for example, gas is typically applied first through uppermost gas inlet 41b continuously as vacuum is applied to vacuum extraction pipe 30 until two-phase flow is established within vacuum extraction pipe 30 from the depth of gas inlet 41b. At this point, the flow of gas through the inlet next in depth, which in Figure 3 is gas inlet 41a, is initiated and maintained until two-phase flow is established within vacuum extraction pipe 30 from the depth of gas inlet 41a. Subsequently, the flow of gas through the inlet next in depth, which in Figure 3 is gas inlet 41c, is initiated and maintained until two-phase flow is established within vacuum extraction pipe 30 from the depth of gas inlet 41c. The flow of gas through each inlet can be terminated once two-phase flow is established from that depth, although it is preferred to maintain at least some overlap between the flow of gas through one inlet and the flow of gas through the inlet next in depth to ensure that two-phase flow does not cease in the vacuum extraction pipe at any time. For example, in a particular well, gas might be introduced first through uppermost gas inlet 41b for a period of about 10 seconds, after which two-phase flow is established within the vacuum extraction tube from the depth of gas inlet 41b, followed by maintaining gas flow through gas inlet 41b while also permitting gas to flow through gas inlet 41a for a period of about 5 seconds, followed by terminating the flow through gas inlet 41b while allowing gas to continue to flow through gas inlet 41a for a period of 15 seconds, after which two-phase flow is established within the vacuum extraction tube from the depth of gas inlet 41a, followed by maintaining gas flow through gas inlet 41a while also permitting gas to flow through gas inlet 41c for a period of about 5 seconds, followed by terminating the flow through gas inlet 41a while allowing gas to continue to flow through gas inlet 41c for a period of 20 seconds, after which two-phase flow is established within the vacuum extraction tube from the depth of gas inlet 41c, followed by terminating the flow through gas inlet 41c. The duration of flow through each inlet and the duration of overlap for flow from two or more inlets will vary with each well. It is also possible, however, to initiate flow through each inlet sequentially, with no overlap between the flow through one inlet and the flow through another inlet, or to initiate flow in multiple inlets in some order other than sequentially by increasing depth. Further, flow through multiple gas inlets can be initiated simultaneously. If desired, the flow duration through each gas inlet can be controlled automatically by running each gas inlet 41a, 41b, and 41c through a timer control system. Generally, flow through the gas inlet or inlets is ceased once the two-phase vacuum extraction process has been successfully initiated. At various times in the extraction process, however, the flow through vacuum extraction pipes 30a, 30b, and/or 30c may vary from the desired two-phase flow to some other form of flow, such as slug flow. At these times, gas may also be introduced through gas inlet or inlets 41 to convert the flow in the vacuum extraction pipe 30 back to the desired two-phase form. The gas inlet or inlets can be of any suitable configuration, with a few examples of suitable configurations being illustrated schematically (and not necessarily to scale) in Figures 5, 6, and 7. As illustrated schematically in Figure 5, gas inlet 41a enters vacuum extraction pipe 30 through an opening in the side of vacuum extraction pipe 30 and terminates at an approximate right angle to the wall of vacuum extraction pipe 30. While not required, it is preferred that the opening of gas inlet 41a be situated in relative close proximity to the inner wall of vacuum extraction pipe 30 to minimize frictional forces as air 51 is introduced into vacuum extraction pipe 30 through gas inlet 41a to initiate two-phase flow of gas 53 and liquid 55 in vacuum extraction pipe 30. As illustrated schematically in Figure 6, gas inlet 41a' enters vacuum extraction pipe 30 through an opening in the side of vacuum extraction pipe 30 and terminates at an approximate parallel angle to the wall of vacuum extraction pipe 30. While not required, it is preferred that the opening of gas inlet 41a' be situated in relative close proximity to the inner wall of vacuum extraction pipe 30 to minimize frictional forces as air 51 is introduced into vacuum extraction pipe 30 through gas inlet 41a' to initiate two-phase flow of gas 53 and liquid 55 in vacuum extraction pipe 30. As illustrated schematically in Figure 7, gas inlet 41c enters vacuum extraction pipe 30 through the bottom opening of vacuum extraction pipe 30 and terminates at an approximate parallel angle to the wall of vacuum extraction pipe 30. While not required, it is preferred that the opening of gas inlet 41c be situated in relative close proximity to the inner wall of vacuum extraction pipe 30 to minimize frictional forces as air 51 is introduced into vacuum extraction pipe 30 through gas inlet 41c to initiate two-phase flow of gas 53 and liquid 55 in vacuum extraction pipe 30. The optional gas inlet or inlets 41 can be either flexible or rigid, and can be of any suitable material, such as polymers and plastics, including polyvinyl chloride, Teflon®, polyethylene, polypropylene, or the like, metals, such as stainless steel, galvanized steel, copper, brass, or the like, or any other suitable material. The gas inlet or inlets 41 can be of any desired or suitable dimensions to enable the desired rate of flow through the vacuum extraction pipe, and typically will vary depending on the dimensions of the vacuum extraction pipe, the depth of the well, the nature of the packing around the well, and the like. Any desired pressure can be employed for the gas introduced into vacuum extraction pipe 30 through gas inlet or inlets 41. Typical pressures range from atmospheric pressure outside the well (in which case no air compressor is required) to about 100 pounds per square inch, with preferred pressures being from about 20 to about 60 pounds per square inch, more preferably from about 30 to about 50 pounds per square inch, although the pressure can be outside these ranges. Greater pressures initiate two-phase flow within the vacuum extraction pipe more rapidly, and may also be more desirable at greater relative depths of water (with relative depth in this instance referring to the difference in depth between the gas inlet and the groundwater level within the vacuum extraction pipe). Any desired gas can be introduced into the vacuum extraction pipe through the optional gas inlet or inlets. Ambient air may be selected as the most inexpensive gas. In addition, the air introduced through gas inlet or inlets 41 can, if desired, be heated to improve the extraction of some contaminants. Further, gas inlet or inlets 41 can be used as an inlet for introducing other materials or chemicals into the riser pipe and extraction stream for chemically or otherwise interacting with the water and air mixture. For example, oxidizers or surfactants or other chemicals can be introduced for the treatment of water-borne or vapor-borne contaminants removed by the vacuum extraction pipe. Additionally, in situations wherein the apparatus and process of the present invention are employed in conjunction with a biotransformation process, wherein soil contaminants are biologically transformed into innocuous materials by interaction with bacteria or other biological methods, the gas inlet or inlets can be employed to introduce into the vacuum extraction pipe nutrients for biotransformation, such as cellulose or the like, or for introducing nitrogen to enhance anaerobic processes or oxygen to enhance aerobic processes. Returning to Figures 2, 3, and 4, the upper portions 46 of the riser pipes 44 are surrounded by a low permeability grout, such as bentonite cement 54a, and below the grout 54a by a bentonite seal 56a. Additional layer of grout 54b and additional layer of bentonite cement 56b isolate the terminal ends of vacuum extraction pipe 30c and vacuum extraction pipe 30b, thus also isolating fracture 22 from fracture 24. Additional layer of grout 54c and additional layer of bentonite cement 56c isolate the terminal ends of vacuum extraction pipe 30b and vacuum extraction pipe 30a, thus also isolating fracture 24 from fracture 26. Relatively low permeability sand 49 is situated within borehole 42 and riser pipe 44 between the grout and bentonite layers to support the grout and bentonite layers within the borehole and riser pipe. Sand 49 preferably is also contained within fractures 22, 24, and 26 to prevent collapse of the fractures The area within the borehole 42 surrounding the slotted lower portions 48 of the riser pipes 44 and part of the upper portions 46 above the slotted lower portions 48 is packed with fine screened sand 49, to facilitate the flow of gas and liquid from the surrounding soil into the riser pipes 44. Figure 8 (not drawn to scale) illustrates schematically an example of an optional air inlet probe 27. The air inlet probe 27 comprises a borehole 58, which receives a pipe 60. The pipe 60 in one operative embodiment comprises a four inch diameter PVC pipe, capped at the bottom, and having a screen of 0.010 inch slots. The pipe 60 is surrounded at its upper end by a cement collar or bentonite seal 62, extending to the ground surface 64. Any suitable valve 68 can be provided in association with the air inlet probe 27 to open or close the air injection probe as desired. Surrounding a medal portion 70 of the pipe 60 within the borehole 58 is a bentonite slurry 72, which provides a gas-tight seal between the pipe 60 and the borehole 58. The slotted lower portion 74 of the pipe 60 is surrounded by gas-permeable packed sand 76. As will now be apparent, the pipe 60 facilitates the injection of air into a preferential flow path (preferential flow path 22 shown in this Figure).

Claims: A process for removing contaminants from a contaminated area (12) of the ground comprising soil having a first permeability, said ground having a plurality of paths (22,24,26) of preferential flow, each path (22,24,26) having a permeability at least ten times greater than the first permeability, which process comprises providing a borehole in the contaminated area (12) to intersect at least a first path (22) of preferential flow and a second path (24) of preferential flow, said second path (24) of preferential flow being situated at a depth greater than said first path (22) of preferential flow; placing in the borehole a first vacuum extraction pipe (30c) having a bottom opening situated within the first path (22) of preferential flow and a second vacuum extraction pipe (30b) having a bottom opening situated within the second path (24) of preferential flow; isolating the first path (22) of preferential flow from the second path (24) of preferential flow so that a vacuum applied to the first vacuum extraction pipe (30c) with a bottom opening situated in the first path (22) of preferential flow will extract gases and liquids from the first path (22) of preferential flow but not from the second path (24) of preferential flow and a vacuum applied to the second vacuum extraction pipe (30b) with a bottom opening situated in the second path (24) of preferential flow will extract gases and liquids from the second path (24) of preferential flow but not from the first path (22) of preferential flow; applying a vacuum to at least one of the vacuum extraction pipes (30a,30b,30c) to draw gases and liquid from at least one of the paths (22,24,26) of preferential flow into a vacuum extraction pipe (30a,30b,30c) and transport both the gases and the liquid to the surface as a common stream; forming from the common stream a stream which is primarily liquid and a stream which is primarily gaseous; and removing contaminants from at least one of the liquid stream and the gaseous stream. A process as claimed in claim 1, wherein the ground has a vadose zone and a water table, the borehole extends to a depth below the water table, the first vacuum extraction pipe (30c) is situated within a first riser pipe (44c) having perforations situated within the first path (22) of preferential flow, the second vacuum extraction pipe (30b) is situated within a second riser pipe (44b) having perforations situated within the second path (24) of preferential flow, and the perforations of at least one riser pipe (44a,44b,44c) are situated at least below the water table. A process as claimed in claim 2, wherein the perforations in at least one riser pipe (44a,44b,44c) are situated only below the water table; or wherein the perforations in one of the riser pipes (44a,44b,44c) are situated both in the vadose zone and below the water table; or wherein the perforations in at least one riser pipe (44a,44b,44c) are situated only in the vadose zone above the water table. A process as claimed in any one of claims 1 to 3, wherein,the soil has a permeability of about 1 × 10 -4 centimeters per second or less; and/or wherein the paths (22,24,26) of preferential flow have a permeability of about 1 × 10 -3 centimeters per second or greater. A process as claimed in any of claims 1 to 4, wherein at least one of the preferential flow paths (22,24,26) is created by a hydraulic fracturing process. A process as claimed in any of claims 1 to 5, wherein at least one inlet probe (27) is provided which allows introduction into at least one of the paths (22,24,26) of preferential flow of a fluid from a location spaced from the borehole. A process according to claim 6, wherein a fluid is introduced into the first path (22) of preferential flow through an air inlet probe (27) while vacuum is applied to the first vacuum extraction pipe (30c); or wherein a fluid is introduced into the second path (24) of preferential flow through an air inlet probe (27) while vacuum is applied to the first vacuum extraction pipe (30c); or wherein a fluid is introduced into the first path (22) of preferential flow through an air inlet probe (27) while vacuum is applied to the second vacuum extraction pipe (30b); or wherein a fluid is introduced into the second path (24) of preferential flow through an air inlet probe (27) while vacuum is applied to the second vacuum extraction pipe (30b); or wherein a fluid is introduced simultaneously into the first path (22) of preferential flow and the second path (24) of preferential flow through at least one air inlet probe (27) while vacuum is applied simultaneously to the first vacuum extraction pipe (30c) and the second vacuum extraction pipe (30b). A process according to claim 1 wherein a fluid is introduced into the first vacuum extraction pipe (30c) while vacuum is applied to the second vacuum extraction pipe (30b); or wherein a fluid is introduced into the second vacuum extraction pipe (30b) while vacuum is applied to the first vacuum extraction pipe (30c). A process according to claim 1 wherein vacuum is applied simultaneously to the first (30c) and second (30b) vacuum extraction pipes. An apparatus for removing contaminants from a contaminated area (12) of the ground comprising soil having a first permeability, said ground having a plurality of paths (22,24,26) of preferential flow, each path having a permeability at least ten times greater than the first permeability, said contaminated area (12) of the ground being provided with a borehole extending downwardly from the surface of the ground to intersect at least a first path (22) of preferential flow and a second path (24) of preferential flow, said second path (24) of preferential flow being situated at a depth greater than said first path (22) of preferential flow, said apparatus comprising at least a first vacuum extraction pipe (30c) and a second vacuum extraction pipe (30b) situated inside of the borehole, wherein the first vacuum extraction pipe (30c) has a bottom opening situated within the first path (22) of preferential flow and the second vacuum extraction pipe (30b) has a bottom opening situated within the second path (24) of preferential flow, said first path (22) of preferential flow being isolated from said second path (24) of preferential flow so that a vacuum applied to the first vacuum extraction pipe (30c) with a bottom opening situated in the first path (22) of preferential flow will extract gases and liquids from the first path (22) of preferential flow but not from the second path (24) of preferential flow and a vacuum applied to the second vacuum extration pipe (30b) with a bottom opening situated in the second path (24) of preferential flow will extract gases and liquids from the second path (24) of preferential flow but not from the first path (22) of preferential flow; a vacuum-forming apparatus (32) in fluid communication with the first vacuum extraction pipe (30a) and the second vacuum extraction pipe (30b) and adapted to form a zone of reduced pressure in the first (22) and second (24) paths of preferential flow around the borehole, whereby gases and liquid can be drawn from the first (22) and second (24) paths of preferential flow into a vacuum extraction pipe (30a,30b,30c) and conveyed to the surface as a common stream; a vapor-liquid separator in fluid communication with said vacuum-forming apparatus (32) and said first (30c) and second (30b) vacuum extraction pipes, wherein said vapor-liquid separator separates the common stream into separate gas and liquid streams; and a contaminant removal system, (36) said contaminant removal system (36) being situated to remove contaminants from at least one of the liquid stream and the gas stream.

Inventors: DUFFNEY ELLIOTT N, HESS RONALD E, HUBER SCOTT M, TORNATORE PAUL M, DUFFNEY, ELLIOTT N., HESS, RONALD E., HUBER, SCOTT M., TORNATORE, PAUL M.
Applicants: XEROX CORP, XEROX CORPORATION
Application year: 1995
Main classification: B09C1
IPC codes: E21B43, B09C1, B01D53