Apparatus and methods for removing contaminants

Abstract: A method and apparatus are disclosed for removing contaminants from the ground using vacuum extraction. Specifically, a circuit (400) is disclosed that can control the flow of atmospheric air into a vacuum extraction well (114). By controlling the air flow into the well, the air flow circuit serves to regulate the vacuum that is applied to sub-surface contaminants. This vacuum lifts the contaminated effluent from the ground, so it can be subjected to further processing.

Description: This invention relates generally to removing contaminants from effluent. The 2-PHASE™ (a trademark of the Xerox Corporation) extraction process provides a method and apparatus for removing chemicals and other undesirable substances from a contaminated area of the ground. Generally speaking, an extraction tube or the like is placed within the contaminated area and a vacuum is applied such that a combined liquid and vapor stream is drawn from the ground through the tube. The liquid and vapor are then separated, and each phase is treated to remove contaminants. Such processes are disclosed in US-A 5,464,309, US-A 5,441,365, US-A 5,358,357, US-A 5,197,541, US-A 5,172,764, and US-A 5,050,676, all assigned to Xerox Corporation, Stamford, Connecticut, the assignee of the present invention. Contaminants can be found in subsurface soil and groundwater, in the liquid or vapor phase. They can exist as discrete substances, or they can be mixed with and/or dissolved in groundwater and soil vapors. Various types of contaminants can be found in groundwater and soil, including volatile organic compounds, semi-volatile materials, metal contaminants, and the like. Such contaminants can be found in the vadose zone (the unsaturated layer that lies between the surface of the earth and the water table), at the interface between the vadose zone and the water table, and in the saturated zone below the water table. A variety of techniques have been used for removal of contaminants and remediation of affected media. One technique entails the excavation and off-site treatment of the soil. Another technique entails saturating the contaminated soil with water in situ, causing the contaminants to be leached slowly from the soil by the water. The contaminated water can then be removed. US-A-3491510 discloses a method and apparatus for retrieving oil from a producing zone, where artificial lift is required to bring the oil to the surface, using compressed air to force the oil to the surface. EP-A-0304712 discloses a method of driving impurities from the ground including an air control circuit in fluid communication with an extraction well for sustaining a vacuum within a vacuum extraction pipe. US-A 5,464,309 discloses certain aspects of the 2-PHASE™ extraction process for removing volatile organic chemicals from a contaminated area of the ground. A borehole is placed in the contaminated area to a depth below the water table, and a plurality of concentric pipes are placed in the borehole. Gas and a vacuum are simultaneously applied to the pipe system such that contaminated vapors and liquid are drawn from the soil into the pipes. The vapors and liquids are transported to the surface together and separated into two components. Each stream is treated to remove the contaminants. An apparatus for carrying out the process is also disclosed. US-A 5,358,357 discloses other aspects of the 2-PHASE™ extraction process and apparatus in which vacuum extraction is used to remove soil contaminants in both the saturated and vadose zones. A borehole is provided in the contaminated area to a depth below the water table, a vacuum extraction pipe is placed inside of a riser pipe and both pipes are placed into the borehole to a depth below the water table. The vacuum extraction pipe has at least one gas inlet situated below the groundwater level. A gas is introduced into the riser pipe while a vacuum is being introduced into the extraction pipe. Gases and liquid are drawn from the soil into the perforated riser pipe and from the riser pipe into the vacuum extraction pipe. Two-phase flow within the vacuum extraction pipe is initiated when gas is introduced into the vacuum extraction pipe below the groundwater level. Both the vapors and the liquid are transported to the surface as a two-phase common stream. The vapor and liquid streams are then treated to remove contaminants. US-A 5,050,676 and US-A 5,197,541 disclose still other aspects of the 2-PHASE™ extraction process and apparatus used to extract contaminants from the ground, including vacuum withdrawal of liquid and vapor phases as a common stream, separation of the liquid and vapor phases, and subsequent treatment of the separated liquid and vapors to produce clean effluents. Two phase extraction employs a single vacuum generating device to remove contaminants in both the liquid stream and soil gases through a single well casing. The 2-PHASE™ extraction process is a very effective technique for removing volatile and water soluble chemicals from a contaminated area of the ground, but seasonal changes and other natural events which regularly alter the height of the water table can adversely affect its operation. For example, during spring months the amount of groundwater present in a given area will often increase due to snow melt or precipitation run off. Since a greater volume of contaminated effluent must be extracted from sub-surface soil, the ratio of entrainment air to groundwater must be manipulated manually or the anti-gravitational force being applied to the effluent stream will be too small to lift it from the ground. During the summer, groundwater levels typically decrease, resulting in an increase in the depth of the vadose zone. This means that the amount of contaminated groundwater in the area will decrease and the amount of soil gas present will increase. This additional soil gas results in greater air flow within the extraction well. The increase in the flow of air causes a loss of vacuum which makes well operation inefficient. In any season, the bottom of the extraction well must be kept at or very near the liquid-vapor interface within the well in order to maintain the entrainment of suspended liquid within the extracted air stream. If the liquid-vapor interface drops below the bottom of the well, the amount of air being supplied to the well must again be adjusted if the vacuum condition is to be maintained. Once ground water levels rise, the air supply must again be adjusted to optimize the vacuum or the extraction well will again operate inefficiently. Thus, entrainment air must be adjusted as the groundwater level fluctuates if optimal vacuum delivery to the well formation is to be maintained, and efficient operation of the extraction well is to continue. The vacuum within the well is currently maintained by supplying atmospheric air through an inlet as the level of groundwater increases. As the groundwater level drops, the air supply is cut-off. This method of operation requires a technician or other maintenance person to physically travel out to the well site, and inspect the hardware to see if the well is operating properly. If the liquid is no longer being entrained, the technician must manually supply compressed air to the well to restart it. The valve must then be manually adjusted to vary the flow of ambient air once the well begins to operate. Because a failure will not be detected until a physical inspection of the hardware is performed, the well may be inoperable for extensive periods of time. It is desirable to provide a way to automatically direct and regulate the amount of air that is applied to the well and extraction tube, as seasonal and other changes to the groundwater level take place. The present invention provides such means, thereby eliminating the need for human intervention and the costs and inconvenience associated with it. Accordingly, although known apparatus and processes are suitable for their intended purposes, a need remains for processes and apparatus for removing contaminated liquids and gases from soil with increased efficiency. Further, there is a need for apparatus and methods for automatically adjusting the amount of air that is supplied to the vacuum extraction well, so as to maintain the appropriate vacuum conditions throughout its operation. The present invention reduces these problems with air flow control techniques that can be used to maintain the vacuum required to extract contaminated liquids and vapors. In one aspect of the invention, there is provided an apparatus for removing contaminants from a ground water stream, comprising: a vacuum extraction pipe for being placed in an extraction well that contains contaminated ground water, the vacuum extraction pipe having an inlet for being placed into the ground water, an outlet, and a plurality of ports; a riser pipe around said vacuum extraction pipe; a vacuum inducing device in fluid communication with said vacuum extraction pipe at said outlet for drawing the ground water upward through the vacuum extraction pipe; contaminant removing means communicating with said vacuum inducing device and with said vacuum extraction pipe to receive the ground water drawn upward through the vacuum extraction pipe and to remove contaminants from the ground water; characterised by an air flow control circuit, in fluid communication with said extraction well through an inlet in the riser pipe and in fluid communication with said vacuum extraction pipe at said plurality of ports, the air flow control circuit comprising: a conduit having a first end and a second end, each end defining an aperture through which air may pass, said first end of said conduit located inside an inner wall of said riser pipe, and outside an outer wall of said vacuum extraction pipe such that air may move from said conduit through said port into said vacuum extraction pipe and said second end of said conduit connected to the riser pipe through the inlet; an air inlet and a valve associated with the air inlet to control air flow into said conduit; and a check valve assembly situated in said conduit between said inlet of said riser pipe and said port of said vacuum extraction pipe, comprising a housing having a first interior wall and a second interior wall; a stop fixed to said second interior wall and a gate hingedly connected to said first interior wall, and abuttable against said stop. In another aspect of the invention, there is provided a method of removing contaminants from ground water, comprising: (a) applying a vacuum to draw ground water upward from an extraction well through a vacuum extraction pipe having an inlet placed into the ground water, the extraction well including a riser pipe around said vacuum extraction pipe; (b) supplying air to the extraction well to enhance upward movement of ground water; (c) automatically varying the air supply as the level of ground water in the extraction well varies; and (d) removing contaminants from the ground water drawn upward from the extraction well; characterised in that the step of automatically varying the air supply comprises: drawing airthrough an inlet into a conduit that is connected both to the vacuum extraction pipe and the riser pipe; moving the air from the air inlet into the vacuum extraction pipe and the riser pipe; and, automatically controlling the flow of air to vacuum extraction pipe and the riser pipe by the use of a gate valve situated in a branch pipe to the vacuum extractor pipe, wherein the gate valve is responsive to the pressure in the riser pipe and the vacuum extraction pipe, such that the air flow to the vacuum extraction pipe increases as the ground water level rises and decreases as the ground water level sinks. The invention will now be described, by way of example, with reference to the accompanying drawings, in which: FIG. 1 is a schematic view of a typical vacuum extraction apparatus for removing contaminants from the ground; FIG. 2 depicts an elevation view of a typical 2-PHASE™ extraction well; FIG. 3 is an elevation view depicting the aspiration air inlet without the present invention as it is presently attached to the extraction well; FIG. 4 is a detailed view of air flow control circuit of the present invention; and FIG. 5 depicts an elevation view of the present invention attached to an extraction well. The present invention may be used in conjunction with the 2-PHASE™ extraction process and apparatus for removing contaminants and/or contaminant-containing vapors and liquids from the ground. The invention may also be used with other processes, and is therefore not limited to this embodiment. In a typical contaminated area, a source of volatile contaminants creates a plume of adsorbed, dissolved, or suspended free phase and gaseous phase contaminants in the soil of the vadose (unsaturated) zone. The contaminants making up the plume tend to leach or percolate downward toward the natural water table. Components lighter than water and not dissolved tend to float at the top of the water table. Dissolved contaminants tend to percolate downward in a plume below the water table, and free-phase components heavier than water tend to migrate downward to the aquitard. The 2-PHASE™ extraction process generally involves removing liquids and vapors from the ground as a single common stream, separating the vapors in the stream from the liquids, and treating each component to remove contaminants. A vacuum supplies the anti-gravitational force used to extract the effluent mixture from the ground. Referring now to the drawings where the showings are for the purpose of describing an embodiment of the invention and not for limiting same, FIG. 1 illustrates schematically a system, designated generally by the reference numeral 100. A vacuum inducing device 102 is in fluid communication through a pipe 106, vapor-liquid phase separator 108 such as a knock-out pot, and pipe 110 with the pipe fitting 112 to one or more extraction wells 114. Air flow control circuit 400 is attached to extraction well 114 as shown. Vacuum inducing device 102 causes a mixed liquid-vapor stream 104 (illustrated in FIGS. 3 and 4) to be removed from the ground through extraction well 114. This mixed liquid-vapor stream (also referred to as two-phase effluent stream 104) is drawn up from the ground through pipe 110 and into knock-out pot 108. The mixture enters knock-out pot 108 where it is separated into a liquid component and a vapor component. The knock-out pot is then emptied, and either or both components can be subjected to further treatment for removal of additional contaminants. Fig. 1 illustratively shows line 116, through which the liquid component can be removed from knock-out pot 108 by operation of pump 118, which provides the liquid component for treatment to remove contaminants. Fig. 2 depicts a detailed illustration of a typical extraction well 114. Extraction well 114 shown has an elongated borehole 202 with a riser pipe 204 placed inside. Riser pipe 204 contains perforations which lie either entirely below the water table, entirely above the water table, or both above and below the water table. While the illustration depicts vacuum extraction pipe 206 situated inside of riser pipe 204 and with the two pipes approximately concentric, it may be possible for riser pipe 204 to be placed inside of or next to vacuum extraction pipe 206. It is intended to embrace these and other configurations. FIG. 3 depicts a more detailed illustration of extraction well 114, and particularly aspiration air inlet 302 as it currently exists. As shown, air inlet 302 includes valve 304 which controls the flow of atmospheric air into extraction well 114. For efficient entrainment to take place, valve 304 must be opened and closed manually as it becomes necessary to increase or decrease the amount of atmospheric air that enters extraction well 114. Under the current method of operating the 2-PHASE™ extraction process, a vacuum is applied at the top of vacuum extraction pipe 206 such that the effluent stream 104 will be drawn from the ground. At the same time, compressed air is delivered (by apparatus not shown) to the bottom of extraction well 114 to entrain the contaminated groundwater and soil gas. As extraction well 114 continues to operate, maximum vacuum conditions will develop, and the flow of compressed air into the bottom of the well can be reduced to zero. As the volume of groundwater present in the area surrounding the well changes, air must be supplied to or removed from the well in order to sustain the vacuum. One current operating method requires reinitiating the flow of compressed air into extraction well 114 to entrain the added groundwater. Valve 304 is then manually adjusted to draw atmospheric air into extraction well 114. This allows ambient air to entrain the effluent stream and continue to operate the well. Adjustments to the amount of atmospheric air that enters extraction well 114 can be made automatically by the air flow control circuit 400 of the present invention. FIG. 4 is a detailed illustration of the air flow control circuit 400. Air flow control circuit 400 automatically directs and regulates the amount of atmospheric air that enters riser pipe 204 and vacuum extraction pipe 206 so well operation can be sustained throughout the various seasonal changes that take place. Air flow control circuit 400 includes tube 402 connected in air flow relationship to a first side 408 of check valve assembly 406. Check valve assembly 406 includes a housing 416 with a gate 414 hingedly connected to one interior wall 418. Housing 416 has a stop 412 mounted to another interior wall 420 such that gate 414 may either rest against stop 412 in a closed position, or move away from stop 412 to an open position. A first opening of tube 402 is placed inside riser pipe 204, so that it may be attached to vacuum extraction pipe 206 through ports 208 at various locations. This enables the vacuum to draw air from air flow control circuit 400 into vacuum extraction pipe 206. Tube 404 connects a second side 410 of check valve assembly 406 to extraction well 114 at point 306. Point 306 serves as an entry into riser pipe 204. Air inlet 302 and valve 304 are connected to tube 404, between check valve assembly 406 and point 306 such that atmospheric air may be directed into check valve assembly 406, and/or into riser pipe 204. FIG. 5 is a detailed illustration which shows air flow control circuit 400 attached to extraction well 114. One end of tube 402 is placed inside of riser pipe 204 between the inner wall of the riser pipe and the outer wall of vacuum extraction pipe 206. Referring again to FIG. 4, prior to the start of the vacuum extraction process gate 414 rests against stop 412 in the closed position. A vacuum is applied at the top of vacuum extraction pipe 206, and valve 304 is opened to allow atmospheric air from inlet 302 to enter extraction well 114 at point 306. The vacuum inside of extraction well 114, and particularly the resulting horizontal force at point 306, will pull gate 414 toward the well causing it to remain closed. Thus, as long as enough vacuum exists, check valve assembly 406 will prevent air from passing gate 414, and will therefore stop ambient air from entering vacuum extraction pipe 206 through tube 402. Aspiration air may still be drawn into extraction well 114 through air inlet 302 at point 306. When the amount of groundwater surrounding extraction well 114 increases, more air must be introduced into extraction well 114 or the vacuum will not be strong enough to continue to remove the contaminant stream from the ground. The present invention provides a means for automatically supplying, directing and regulating the flow of ambient air to the extraction well, thereby eliminating the need for manual adjustment to maintain well operation, although valve 304 could still be manually adjusted. The excess groundwater surrounding the well causes the vacuum inside extraction well 114 to be reduced. This reduced vacuum results in a decrease in the horizontal force being applied at point 306. The weakened horizontal force causes gate 414 to open, and allows ambient air to flow into vacuum extraction pipe 206 through tube 402 as needed. While the vacuum at point 306 has been lowered, the vacuum being applied to the top of vacuum extraction pipe 206 increases. The resulting pressure differential between the air inside vacuum extraction pipe 206 and that within the surrounding riser pipe 204 will cause ambient air to continue to be drawn past gate 414 through tube 402, and into ports 208 and vacuum extraction pipe 206. As shown in Fig. 5, a plurality of ports 208 can be provided between tube 402 and pipe 206, and tube 402 can extend to the lower end of pipe 206, where an additional port could be provided. The flow of ambient air into vacuum extraction pipe 206 will continue until the volume of air within the pipe is large enough to lift the column of effluent to a level at which the vacuum can draw it upward, and apply a vertical force to the effluent stream sufficient to entrain the effluent stream, and lift it from the ground. On the other hand, a decrease in the amount of groundwater in the area causes an increase in the amount of soil gas that is present inside of extraction well 114. This additional gas inside the well will cause it to "short circuit," and fail to reach the bottom of vacuum extraction pipe 206. The aspiration air should be removed from the well if the contaminant removal process is to remain effective. Under these circumstances, when air flow control circuit 400 reaches maximum vacuum, gate 414 will close. This in turn will prevent atmospheric air from being supplied to the well through tube 402 and ports 208. Eliminating the flow of atmospheric air into tube 402 allows the air that is present within the well to be used to lift the effluent stream from below the surface of the ground. This will allow the well to continuously operate in an efficient manner.

Claims: An apparatus for removing contaminants from a ground water stream, comprising: a vacuum extraction pipe (206) for being placed in an extraction well (114) that contains contaminated ground water, the vacuum extraction pipe having an inlet for being placed into the ground water, an outlet, and a plurality of ports (208); a riser pipe (204) around said vacuum extraction pipe; a vacuum inducing device (102) in fluid communication with said vacuum extraction pipe at said outlet for drawing the ground water upward through the vacuum extraction pipe; contaminant removing means (108) communicating with said vacuum inducing device and with said vacuum extraction pipe to receive the ground water drawn upward through the vacuum extraction pipe and to remove contaminants from the ground water; characterised by an air flow control circuit (400), in fluid communication with said extraction well through an inlet (306) in the riser pipe and in fluid communication with said vacuum extraction pipe at said plurality of ports, the air flow control circuit (400) comprising: a conduit (402,404) having a first end and a second end, each end defining an aperture through which air may pass, said first end of said conduit located inside an innerwall of said riser pipe, and outside an outer wall of said vacuum extraction pipe such that air may move from said conduit through said port into said vacuum extraction pipe, and said second end of said conduit connected to the riser pipe through the inlet (306); an air inlet (302) and a valve (304) associated with said air inlet to control air flow into said conduit (402,404); and a check valve assembly (406) situated in said conduit between said inlet of said riser pipe and said port of said vacuum extraction pipe, comprising a housing (416) having a first interior wall (418) and a second interior wall (420); a stop (412) fixed to said second interior wall and a gate (414) hingedly connected to said first interior wall, and abuttable against said stop. An apparatus according to claim 1 in which the contaminant removing means comprises: a vapour-liquid separator (108) to separate the ground water into a liquid component and a vapour component, and to produce said vapour component at a first outlet thereof and said liquid component at a second outlet thereof; a vapour contaminant removal system which receives said vapour component of the ground water from said vapour-liquid separator and reduces a contaminant level within said vapour component; and a liquid contaminant removal system which receives said liquid component of the ground water stream from said vapour-liquid separator and reduces a contaminant level within said liquid component. A method of removing contaminants from ground water, comprising: (a) applying a vacuum to draw ground water upward from an extraction well (114) through a vacuum extraction pipe (206) having an inlet (208) placed into the ground water, the extraction well (114) including a riser pipe (204) around said vacuum extraction pipe (206); (b) supplying air to the extraction well (114) to enhance upward movement of ground water; (c) varying the air supply as the level of ground water in the extraction well (114) varies; and (d) removing contaminants from the ground water drawn upward from the extraction well (114); characterised in that the step of varying the air supply comprises: drawing air through an inlet (302 into a conduit that is connected both to the vacuum extraction pipe (206) and the riser pipe (204); moving the air from the air inlet (302) into the vacuum extraction pipe (206) and the riser pipe (204); and, automatically controlling the flow of air to vacuum extraction pipe (206) and the riser pipe (204) by the use of a gate valve (414), situated in a branch pipe (402) to the vacuum extraction pipe (206), wherein the gate valve is responsive to the pressure in the riser pipe and the vacuum extraction pipe, such that the air flow to the vacuum extraction pipe (206) increases as the ground water level rises and decreases as the ground water level sinks. A method according to claim 3 in which the act of removing contaminants comprises: collecting the ground water in a vapour-liquid separator (108) after the ground water is drawn upward from the extraction well (114); separating the ground water into a liquid component and a vapour component; removing said vapour component of the ground water from a first outlet of said vapour-liquid separator and treating said vapour component of the ground water to remove contaminants; and removing said liquid component of the ground water from a second outlet of said vapour-liquid separator and treating said liquid component of the ground water to remove contaminants. A method according to claim 3 or 4, wherein air drawn through the inlet is ambient air.

Inventors: HESS RONALD E, SALOTTI MICHAEL T, WILLIAMS RICHARD A, HESS, RONALD E., SALOTTI, MICHAEL T., WILLIAMS, RICHARD A.
Applicants: XEROX CORP, XEROX CORPORATION
Application year: 1997
Main classification: B09C1
IPC codes: E21B43, B09C1