Vertical isolation system for two-phase vacuum extraction of soil and groundwater contaminants

Abstract: A process and apparatus for removing contaminants from a contaminated area (12) of the subsurface (18,20) which comprises providing a borehole (42) in the contaminated area; placing in the borehole a perforated riser pipe (44) inside of which is situated a vacuum extraction pipe (30) with an opening situated within the perforated riser pipe, wherein a packing (61) is situated in a portion of the annular space between the vacuum extraction pipe and the perforated riser pipe; applying a vacuum to the vacuum extraction pipe to draw gases and liquid from the subsurface into the perforated riser pipe below the packing and from the riser pipe into the 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.

Description: The present invention is directed to processes for extracting contaminants from soil liquids and gases according to the preamble of claim 1. DE 4240969 discloses a system for and a method of redeveloping contaminated areas of the subsurface. An inflatable packer is actuated to send a portion of the well so as to remove contaminated air from the portion of the well below the packer, and to reintroduce the removed air after filtering and cleaning. EP 0586005 discloses a method and an apparatus for extracting a spilled fluid from a subsurface of earth, wherein a slideable extraction pipe is provided to adjust the length of a perforated portion of an outer tube so as to extract fluid from the borehole. Further, it may be desirable to reduce or eliminate preferential flow through higher permeability zones and allow for depth manipulation of vacuum delivery to the strata surrounding an extraction well. Preferential flow paths of soil gas to the extraction well volatilize and remove contaminants from those preferential flow zones only, while the adjacent lower permeability areas may realize little or no soil gas and/or groundwater movement. Higher permeability materials such as those used to bed subgrade utility conveyance lines and construction fill materials may also "short-circuit" the flow of soil gas through the contaminated zone where vacuum delivery and soil gas and/or groundwater extraction is desired. It may be desired to allow for the delivery of vacuum to lower permeability zones and not to surrounding higher permeability zones. It may also be desired to prevent the establishment of preferential flow paths in the soil surrounding an extraction well. It may further be desired to allow for the removal of soil gases and liquids through selected areas throughout the vertical extent of an extraction well and its radius of influence, resulting in the removal of contamination from areas that would otherwise be compromised by preferential flow. In addition, it may be desired to reduce or eliminate "venting" in an extraction borehole, wherein atmospheric air is drawn through high permeability topsoil directly into the borehole near the surface and from the borehole down into a perforated riser pipe therein, rather than being drawn through the soil to the level of the perforations within the riser pipe and then into the borehole at that level. Further, it may be desired to increase the number of extraction wells which can be in fluid communication with a single vacuum system; since vacuum systems are frequently limited by the number of cubic feet per minute of gas which can be passed therethrough, by reducing the number of cubic feet per minute drawn from each well, more wells can be used with a single vacuum system. Additionally, it may be desired to increase the vacuum delivered to the extraction wells, thereby increasing mass removal and increasing the pressure gradient, resulting in a wider zone of vacuum influence. There may also be a need or desire to exert positive pressure on a first well and extract contaminants from a second well, with the ability to control precisely the area and depth where gas enters and exits the zone between the first and second wells. In addition, it may be desired to extract liquids and gases through one or more selected layers of soil or rock which have a relatively greater bonding potential with the contaminants therein to maximize the flow of liquids and gases through those layers. It is an object of the present invention to provide a process and apparatus for removing contaminants from bedrock, groundwater, and soil with the above noted advantages. According to the present invention, there is provided a process for removing contaminants from a contaminated area of the subsurface as defined in claim 1. The present invention will now be described, by way of example, with reference to the accompanying drawings, in which: 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 subsurface in accordance with the present invention when no preferential flow paths in the surrounding soil as yet exist. Figure 2 is a side elevation view in cross section illustrating a general arrangement for vacuum extraction of contaminants from a contaminated area of the subsurface in accordance with the present invention when preferential flow paths in the surrounding soil have been established. Figure 3 is a cross-sectional view in side elevation of an extraction well suitable for the present invention when no preferential flow paths in the surrounding soil as yet exist. Figure 4 is a cross-sectional view in side elevation of an extraction well suitable for the present invention when preferential flow paths in the surrounding soil have been established. The present invention is directed to a process for the removal of contaminants from bedrock, groundwater, and soil. The term "subsurface" is used herein to refer to topsoil, bedrock, and any soil or ground contained therebetween. Contaminants can be present in the vadose zone and/or below the water table. The process includes the steps of providing a borehole in the contaminated area, placing in the borehole a perforated riser pipe in which is situated a vacuum extraction pipe with an opening situated within the perforated riser pipe, applying a vacuum to the riser pipe through the vacuum extraction pipe so as to draw soil gases and entrained liquid into the riser pipe and to transport both the gases and the liquid to the surface through the vacuum extraction pipe, separating the liquid and the gases, and separately subjecting the separated liquid and gases to appropriate treatment. Treated water can be returned to the soil or disposed of in conventional ways. The vacuum extraction pipe is surrounded with a riser pipe. The riser pipe is constructed with perforations (screening) which may be situated below the water table, in the unsaturated (vadose) zone, or both in the saturated and unsaturated zones, as well as within bedrock. In one embodiment, the riser pipe has perforations both above and below the water table. In another embodiment of the invention, the riser pipe is constructed with perforations (screening) extending only below the water table. In yet another embodiment of the invention, the riser pipe is constructed with perforations (screening) extending only 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 two 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, the riser pipe 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 the 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. Figures 1 and 2 illustrate schematically systems 10 for vacuum extraction and treatment in accordance with the invention. Seen in Figure 1 is a source 11 of volatile contaminants, creating a plume 13 of adsorbed, dissolved, or suspended free phase and gaseous phase contaminants in the soil 15 of the vadose (unsaturated) zone. The contaminants making up the plume 13 tend to leach or percolate downwardly toward the natural water table 17. Groundwater is moving in the direction of the arrows 19. Components lighter than water and not dissolved are depicted by the reference numeral 21, and tend to float at the top of the water table. Dissolved contaminants tend to percolate downwardly in a plume 23 below the water table 17, and free-phase components 25 heavier than water tend to migrate downwardly to the aquitard 27. Seen in Figure 2 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 2, 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. In many instances, the permeabilities of soil within the preferential flow paths can be 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. Paths of preferential flow, however, can also be established between areas with only slightly differing permeabilities, since flow will favor the path of least resistance. 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 29 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. Figure 1, extraction well 28 is sunk in the area of the plume 13 and extends through the vadose zone 15 and below the natural water table 17. Figure 2, extraction well 28 is sunk in 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 32, preferably designed to generate high vacuum conditions, typically from about 17.8 cm to about 73.7 cm (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 any appropriate discharge point as indicated at 38. Contaminants can be stored in drums 40 for eventual destruction or further processing. Figures 3 and 4 illustrate embodiments of extraction well 28 in greater detail. In Figures 3 and 4, the extraction well 28 includes an elongated borehole 42, into which is placed a perforated riser pipe 44 capped at the bottom. The riser pipe 44 is perforated either above the water table, below the water table, or both below and above the water table. In the embodiments illustrated, the riser pipe includes an imperforate upper portion 46 and a perforate (screened) lower portion 48. The riser pipe 44 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 0.010 inch (0.25 mm) slots. Situated inside riser pipe 44 is vacuum extraction pipe 30. The vacuum extraction pipe 30 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 end of the riser pipe 44 is associated with a concrete floor or deck, and is provided with a suitable pipe fitting 52, enabling the riser pipe 44 and the vacuum extraction pipe 30 to be coupled to the remainder of the vacuum extraction system 32 (not seen in Figures 3 and 4), with vacuum extraction pipe 30 being in fluid communication with the vacuum extraction system. Vacuum extraction pipe 30 can have a bottom opening within the riser pipe 44 either below the water table, at the water table level, or above the water table. While not necessary, it is preferred that the bottom of vacuum extraction pipe 30 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 pipe 30 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 Figure 4, the preferential flow paths 22, 24, and 26 are isolated from each other by layers of relatively impermeable soil (or rock) and, within the borehole, by essentially impermeable seals surrounding the impermeable portion 46 of riser pipe 44. For example, preferential flow path 22 is isolated within borehole 42 and riser pipe 44 by grout layers 54a and 54b and by bentonite cement layers 56a and 56b. Preferential flow path 24 is isolated from preferential flow paths 22 and 26 within borehole 42 and riser pipe 44 by grout layers 54b and 54c and by bentonite cement layers 56b and 56c. Sand 49 situated within the borehole 42 supports the bentonite cement and grout layers within the borehole 42 and riser pipe 44. 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. 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 riser pipe 44, 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 pipe 44. 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 pipe 30 to air inlet 31, or the like. The air flow rate through air inlet 31 can range from nearly zero to any value less than the CFM (or cubic meters per minute) rated capacity of the vacuum pump connected to vacuum extraction pipe 30. While some air flow may be desired 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 air inlet 31 and maximum vacuum being applied to the subsurface soil and water. In addition, the air introduced through air inlet 31 can, if desired, be heated to improve the extraction of some contaminants. Further, air inlet 31 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. Liquid drawn up through vacuum extraction pipe 30 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 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 1 foot (0.3 m) per second to about 200 feet (61 m) per second or greater generally suffice. Vacuum extraction pipe 30 can optionally be equipped with at least one gas inlet 41. As illustrated in Figures 3 and 4, vacuum extraction pipe 30 is equipped with a single optional gas inlet 41. More specifically, as shown in Figures 3 and 4, 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. 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 Figures 3 and 4, 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 (13.8 N/cm 2 to about 41.4 N/cm 2 ) are from about 15 to about 20 seconds when the groundwater level is less than 15 feet (4.6 m) deep and about 45 seconds when the groundwater level is from about 18 (5.5 m) to about 25 feet (7.6 m) 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 pipe 30 is equipped with a multiplicity of gas inlets, gas is typically applied first through the uppermost gas inlet 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 the uppermost gas inlet. At this point, the flow of gas through the inlet next in depth is initiated and maintained until two-phase flow is established within vacuum extraction pipe 30 from the depth of this gas inlet. Subsequently, the flow of gas through the inlet next again in depth is initiated and maintained until two-phase flow is established within vacuum extraction pipe 30 from the depth of this next gas inlet. 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 the uppermost gas inlet for a period of about 10 seconds, after which two-phase flow is established within the vacuum extraction tube from the depth of the uppermost gas inlet, followed by maintaining gas flow through the uppermost gas inlet while also permitting gas to flow through the gas inlet next in depth for a period of about 5 seconds, followed by terminating the flow through the uppermost gas inlet while allowing gas to continue to flow through the gas inlet next in depth for a period of 15 seconds, after which two-phase flow is established within the vacuum extraction tube from the depth of this next gas inlet, and the like for any additional inlets. 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 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 the vacuum extraction pipe 30 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. As illustrated schematically in Figures 3 and 4, gas inlet 41 enters vacuum extraction pipe 30 through an opening in the side of vacuum extraction pipe 30 the bottom opening of vacuum extraction pipe 30. While not required, it is preferred that the opening of gas inlet 41 be situated in relative close proximity to the inner wall of vacuum extraction pipe 30 to minimize frictional forces as air is introduced into vacuum extraction pipe 30 through gas inlet 41 to initiate two-phase flow of gas and liquid in vacuum extraction pipe 30. Additional suitable configurations for gas inlet 41 are disclosed in, for example, US-A-5,358,357. 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 (69 N/cm 2 ), with preferred pressures being from about 20 to about 60 pounds per square inch (13.8 N/cm 2 to about 41.4 N.cm 2 ), more preferably from about 30 to about 50 pounds per square inch (20.7 N/cm 2 to about 34.5 N/cm 2 ), 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 3 and 4, the upper portion 46 of the riser pipe 44 is surrounded by a seal, which comprises a low permeability grout, such as bentonite cement (54 in Figure 3, 54a in Figure 4), and below the grout a bentonite seal (56 in Figure 3, 56a in Figure 4). As shown in Figure 4, additional seals (additional layer of grout 54b and additional layer of bentonite cement 56b) isolate preferential flow path 22 from preferential flow path 24, and additional seals (additional layer of grout 54c and additional layer of bentonite cement 56c) isolate preferential flow path 24 from preferential flow path 26. Relatively low permeability sand 49 is situated within borehole 42 between the seal layers to support the seal layers within the borehole. When preferential flow paths are created intentionally as fractures, 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 portion 48 of the riser pipe 44 and part of the upper portion 46 above the slotted lower portion 48 is packed with fine screened sand 49, to facilitate the flow of gas and liquid from the surrounding soil into the riser pipe 44. Packing 61 is situated between vacuum extraction pipe 30 and riser pipe 44 and is capable of filling a portion of the annular space between the outer diameter of vacuum extraction pipe 30 and the inner diameter of riser pipe 44 and isolating the area below packing 61 from the area above packing 61 in the space between vacuum extraction pipe 30 and riser pipe 44. (By a portion of the annular space it is meant that the packing does not extend for the entire vertical depth of the well, but isolates one vertical portion of the well from another vertical portion of the well.) Packing 61 can be any suitable packing, gasket, or seal which enables vacuum applied from vacuum extraction pipe 30 to be isolated from the area between the riser pipe and the vacuum extraction pipe which is above the packing. One or more packings 61 can be present within riser pipe 44. Examples of suitable configurations include inflatable bladders, solid rubber, plastic, or metal members, one or more O-rings or other cylindrical rings, dynamic packings such as those employed in hydraulic equipment, piston packings, rod or shaft packings, plunger packings, spring-loaded packings, flange packings, nested V rings, conical rings, soft packings, jamb packings, plastic packings, automatic packings, oil seals, pneumatic or inflatable packings, or the like. In one embodiment, packing 61 can be actuatable, enabling the packing to be moved easily within riser pipe 44 and/or around vacuum extraction pipe 30 before actuation of the seal between the vacuum extraction pipe and the riser pipe. Actuation can be by any desired method, such as filling of a bladder with a fluid (which can be a liquid, a gas, a gel, or the like), expansion of a solid expandable material, or the like. Packing 61 can be either permanently or removably attached to either vacuum extraction pipe 30, riser pipe 44, or both, and can be either stationary or positionally variable in depth within the riser pipe. In one preferred embodiment, one or more packings 61 are attached to vacuum extraction pipe 30 and the depth of packing 61 within riser pipe 44 is adjustable by adjusting the depth of the opening of vacuum extraction pipe 30 within riser pipe 44. In another preferred embodiment, one or more packings 61 are not permanently affixed to either vacuum extraction pipe 30 or to riser pipe 44, but are suspended within riser pipe 44 around vacuum extraction pipe 30 and can be independently adjusted in depth within riser pipe 44. Also suitable, however, are other configurations, such as one or more packings 61 attached to riser pipe 44 through which vacuum extraction pipe 30 passes and which permit adjustment of the depth of vacuum extraction pipe 30 within riser pipe 44, or the like. Optional gas inlet 41 can, if desired (and as illustrated schematically in Figures 3 and 4), pass through packing 61 to enable introduction of air through gas inlet 41 into vacuum extraction pipe 30 at a depth below packing 61. Similarly, optional air inlet 31 can, if desired (and as illustrated schematically in Figures 3 and 4), pass through packing 61 to enable introduction of air through air inlet 31 into the area between vacuum extraction pipe 30 and riser pipe 44 at a depth below packing 61. In soils such as those illustrated schematically in Figure 3, wherein no preferential flow paths have as yet been established, the opening of vacuum extraction pipe 30 and the depth of packing or packings 61 can be adjusted periodically to prevent formation of preferential flow paths. As illustrated schematically in Figure 3, if desired, portions of riser pipe 44 can optionally be further isolated from each other with optional additional seals (in the illustrated embodiment, optional additional low permeability grout layers 54d, 54e, and 54f and/or optional additional bentonite seals 56d, 56e, and 56f). Any suitable impermeability material can be employed for the additional seals. The optional additional seals can be of any desired or effective thickness, typically from about 1 inch (2.54 cm) to several feet (meters) in thickness, preferably from about 2 inches (5 cm) to several feet (meters) (but less than the entire depth of the well) to prevent vapor flow from one isolated zone to another. These additional isolation seals create isolated zones within riser pipe 44 and can be placed at desired intervals throughout the vertical extent of the borehole 42. The isolation units partition sand within the borehole and reduce or eliminate delivery of vacuum to any zone within riser pipe 44 situated above packing 61. A pressure gradient is thus created from outside the borehole to the area within riser pipe 44 below packing 61. Additionally, if desired, optional vacuum probes 63 can be situated between each isolated zone to enable measurement of the vacuum below the isolated zone and to confirm or quantify the extent to which the zone above packing 61 has been isolated from vacuum.

Claims: A process for removing contaminants from a contaminated area (13,23) of the subsurface, comprising the steps: providing a borehole (42) in the contaminated area; placing in the borehole a riser pipe (44) having an upper impermeable portion (46) and a lower perforated portion (48); providing an actuable packing (61) in the riser pipe; supplying a vacuum to the riser pipe to draw gases and liquid from the subsurface into the riser pipe below the packing and transport both the gases and the liquid to the surface as a common stream; characterized in that the process further comprises: arranging a vacuum extraction pipe (39) in the riser pipe, the vacuum extraction pipe having an opening within the perforated portion, the riser pipe and the vacuum extraction pipe forming an annular space therebetween, wherein said packing is arranged in a portion of said annular space; providing an upper seal (54, 56) around the impermeable portion of the riser pipe and at least one seal (54d, 56d - 54f, 56f) around the perforated portion (48), spaced apart from said upper seal (54, 56); situating the packing (61) at the lowermost seal of the at least one seal (54d, 56d - 54f, 56f) and actuating the packing (61) to seal the portion of the borehole (42) above the at least one seal (54d, 56d - 54f, 56f) from a portion below the at least one seal (54d, 56d - 54f, 56f); applying said vacuum via said vacuum extraction pipe to extract gases and liquid from the subsurface forming the borehole below the at least one seal but not from the subsurface forming the borehole above the at least one seal, and deactivating said packing to extract gases and liquid from the subsurface above and below the at least one seal so as to subsequently redevelop the subsurface from bottom to top. A process according to claim 1, wherein the packing is situated at the next upper seal of the at least one seal (54d, 56d - 54f, 56f) after the subsurface has been redeveloped with the packing situated at said lowermost seal of the at least one seal (54d, 56d - 54f, 56f), and wherein the packing is activated to seal the borehole below said next upper seal from the borehole above said next upper seal. A process according to claim 1 or 2, wherein gas is introduced (41) into the riser pipe below the packing while a vacuum is applied to the vacuum extraction pipe. A process according to claim 1 or 3, wherein the subsurface has a vadose zone and a water table, the borehole extends to a depth below the water table and the perforations of the riser pipe are situated only below the water table; or wherein the subsurface has a vadose zone and a water table, the borehole extends to a depth below the water table and the perforations of the riser pipe are situated both in the vadose zone and below the water table; or wherein the subsurface has a vadose zone and a water table and the perforations of the riser pipe are situated only in the vadose zone above the water table. A process according to any of the preceding claims, wherein the contaminated area of the subsurface comprises soil having a first permeability, said subsurface having a plurality of paths of preferential flow, each path having a permeability greater than the first permeability, wherein the borehole intersects 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, wherein the first path of preferential flow is isolated from the second path of preferential flow so that a vacuum applied within 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 when the packing is situated at a depth between the first path of preferential flow and the second path of preferential flow. A process according to any of the preceding claims, wherein the packing is positionally variable in depth within the riser pipe; wherein the packing is actuatable to form and break a seal between the vacuum extraction pipe and the riser pipe; and wherein the packing is actuated by inflation of a bladder with a fluid, and preferably the fluid is a gas.

Inventors: DUFFNEY ELIOTT N, HESS RONALD E, HUBER SCOTT M, MANCINI ALFONSO R, SALOTTI MICHAEL T, THOMASSER JOHN F, WILLIAMS RICHARD A, DUFFNEY, ELIOTT N., HESS, RONALD E., HUBER, SCOTT M., MANCINI, ALFONSO R., SALOTTI, MICHAEL T., THOMASSER, JOHN F., WILLIAMS, RICHARD A.
Applicants: XEROX CORP, XEROX CORPORATION
Application year: 1996
Main classification: B09C1
IPC codes: C02F1, B09C1, E21B43