Abstract:
A bioremediation method and system for destroying or reducing the level of contaminants in a contaminated subterranean body of water includes a plurality of spaced injection sites. The injection sites extend below ground and intersect a body of groundwater. Each of the plurality of injection sites are in communication with a supply of concentrated oxygen. The oxygen is conveyed by a delivery mechanism from the supply of oxygen to the injection points to naturally reduce the contaminants in the groundwater. The amount of oxygen delivered to the groundwater is maintained such that the amount of oxygen in the soil gas vapor is between 15% and 25%.

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
     The present invention claims priority from U.S. Provisional Application No. 60/296,540, entitled “Direct Oxygen Injection Technology Systems”, filed Jun. 6, 2001, U.S. Provisional Application Ser. No. 60/296,528, entitled “Enhanced Dissolved Oxygen Technology Systems”, filed Jun. 6, 2001, and U.S. Provisional Application No. 60/296,609, entitled “Multi-Arrayed Vacuum Recovery Systems”, filed Jun. 6, 2001. 
    
    
     TECHNICAL FIELD 
     The present invention relates generally to a method and system for reducing the level of contaminants in a body of groundwater and more particularly to a bioremediation method and system for groundwater treatment. 
     BACKGROUND ART 
     Groundwater contamination, typically arising from petroleum storage tank spills or from intentional or accidental discharge of liquid hydrocarbons or compositions containing same, has become a problem of increasing concern. This type of contamination occurs not only at industrial complexes, but also in suburban neighborhoods, which would appear to be havens from such phenomena. The source of contamination in suburban neighborhoods or areas is very commonly automobile service station sites at which antiquated or abandoned storage tanks have released gasoline, fuel oils, lubricants, and the like into the local groundwater. Other common sources of such noxious materials can include dry cleaning establishments and/or manufacturers or distributors of the tetrachloroethane which is used in the dry cleaning process. 
     Various remediation techniques have been utilized in the past for the treatment of contaminated groundwater in order to reduce or eliminate the contaminants, such as COCs. One of the most widely used systems is one based on so-called “pump and treat” technology. These systems withdraw the contaminated groundwater and a phase-separated product from a recovery well located in the groundwater and pump it to an above-ground treatment facility. Thereafter, various treatment techniques, as are well known, are used to remove contaminants from the displaced groundwater. These “pump and treat” systems are relatively expensive to install and require that the remaining contaminants, which have been separated from the groundwater, be disposed of in an environmentally friendly manner. These processes further increase the cost of the techniques. 
     One example of a known remediation system is disclosed in U.S. Pat. No. 5,286,141. The &#39;141 patent teaches oxidizing the source of groundwater contamination to harmless constituents by locating a plurality of mutually spaced wells into a groundwater region. A treating flow of hydrogen peroxide solution is provided into the groundwater from one or more wells. The treating flow typically contains reaction surface enhancing reagents, which provide increased surfaces at which the reaction between the hydrogen peroxide and the hydrocarbon contaminants may occur. Further, a catalytic agent is also preferably incorporated into the treating solution or as a pre-injection into the groundwater region to promote the desired reaction between the hydrogen peroxide and hydrocarbons. 
     Recently, there has also been increasing interest in bioremediation technology. However, its use in treating groundwater has been relatively ineffective due to the complexity of the procedures and equipment required, including expensive and complex reactors. Moreover, current bioremediation techniques can cause adverse geochemical reactions and can introduce new toxic compounds into the groundwater. Additionally, current bioremediation systems, still require the use of non-organic catalysts or additives to cause the process to be completed in a reasonable period of time. These catalysts or additives raise other contaminant issues with respect to the groundwater. 
     It is known that naturally growing bacteria in the groundwater can break down groundwater contaminants. However, these bacteria are not always present in large enough quantities to be effective and can also be absent altogether. Moreover, these bacteria feed off oxygen and the lack of oxygen is the single biggest limiting factor on the growth of the bacterial population and therefore contaminant decrease. Ambient air, which is comprised of about 21% percent oxygen, only results in approximately 10-12 ppm of dissolved oxygen in the groundwater and thus is not sufficient to adequately destroy or reduce contaminants. Various attempts to increase the amount of oxygen by utilizing oxygen releasing compounds have been tried, but these oxygen releasing compounds, such as magnesium peroxide or calcium peroxide are expensive. Further, these oxygen releasing compounds only produce a small amount of usable oxygen and therefore do not significantly increase the bacterial population. 
     SUMMARY OF THE INVENTION 
     It is therefore an object of the present invention to provide a bioremediation method and system for groundwater treatment that is more effective than prior bioremediation systems. 
     It is another object of the present invention to provide a bioremediation method and system for groundwater treatment that is less expensive than prior bioremediation systems. 
     It is still another object of the present invention to provide a bioremediation method and system for groundwater treatment that treats contamination naturally and effectively. 
     It is still another object of the present invention to provide a bioremediation system that is relatively easy and inexpensive to install and operate. 
     It is a related object of the present invention to provide a bioremediation system that can be installed with minimal site disturbance or disruptance. 
     In accordance with the above and other objects of the present invention a bioremediation method and system is provided. The method includes providing a plurality of injection points extending from above ground to a subterranean body of groundwater. Substantially pure oxygen is delivered to the plurality of injection points and into the subterranean body of groundwater until the level of contaminants in the groundwater is reduced or eliminated. The amount of oxygen in the soil gas vapor is monitored and the amount of oxygen in the soil gas vapor is maintained between approximately 15% and 25%. 
     The system includes a plurality of injection points extending below ground such that they intersect a body of groundwater. The plurality of injection points are in communication with a supply of concentrated oxygen. The concentrated oxygen is conveyed to each of the plurality of injection points and into the groundwater. The system includes at least one monitoring well for evaluating the level of contaminants in the groundwater. The amount of oxygen in the soil gas vapor is maintained between approximately 15% and 25% to efficiently reduce contaminants in the groundwater. 
     The above objects and other objects, features and advantages of the present invention will be apparent from the following detailed description of best made for carrying out the invention to be taken in connection with the accompanying drawings and appended claims. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  is a schematic illustration of a direct oxygen injection bioremediation system in accordance with a preferred embodiment of the present invention; 
         FIG. 2  is an illustration of a preferred flow meter for use with the system in accordance with the present invention; 
         FIG. 3  is a schematic illustration of the breakdown of contaminants in accordance with the present invention; and 
         FIG. 4  is a schematic illustration of an exemplary direct oxygen injection bioremediation system installation in accordance with a preferred embodiment of the present invention. 
     
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT 
     Referring now to  FIG. 1  which illustrates a bioremediation system  10  in accordance with the present invention. The preferred bioremediation system  10  is preferably used to clean up biodegradable petroleum constituents that are present in contaminated groundwater. However, it should be understood, that the system  10  can be used to clean up other contaminates or constituents in groundwater and that the system may be used for a variety of other purposes. For example, the system  10  may also be used to assist in cleaning up contaminants that may be present in ground soil. 
     The preferred bioremediation system  10  preferably includes a source of oxygen  12 , such as a liquid oxygen tank. However, the oxygen can be provided in a variety of other forms. While the source of oxygen is preferably pure, it need only be of sufficient purity to accomplish the objectives of the present invention. For example, a source of oxygen that has less than 100% and over 50% oxygen may also be sufficient. The source of oxygen  12  is preferably in communication with a control panel  14  to regulate the flow of oxygen, in vapor form, from the oxygen source  12 . The oxygen that flows to the control panel  14  is then conveyed to a plurality of injection sites  16  in a subterranean body of groundwater, generally indicated by reference number  18 . Each of the injection sites  16  can also be placed in communication with a source of microbials to enhance clean-up. The location of the injection sites  16  can be determined in a variety of ways, as discussed below. 
     The source of oxygen  12  is preferably coupled to the control panel  14  by a pressure hose  20  in order to convey the oxygen in vapor form thereto. The pressure hose  20  has a first end  22  that is connected to the source of oxygen  12  and a second end  24  that is connected to the control panel  14 . The source of oxygen  12  has a shut off valve  26  associated therewith, which is located between the source of oxygen  12  and the first end  22  of the pressure hose  20 . The shut off valve  26  allows the flow of oxygen from the source of oxygen  12  to the pressure hose  20  to be manually closed as desired. It should be understood that the valve can also be electronically controlled to regulate the flow of oxygen from the source of oxygen  12 . 
     The second end  24  of the pressure hose  20  is preferably connected to a pressure regulator  28  which allows the pressure of oxygen exiting the source of oxygen  12  to be controlled. In the preferred embodiment, the pressure regulator  28  is set such that the pressure of oxygen exiting the oxygen source  12  is set for example, at 100 psi. It should be understood that the pressure regulator  28  can be adjusted to regulate the flow of oxygen to a variety of different pressures. 
     The oxygen that exits the pressure regulator  28  enters a first conduit  30 , which conveys the pressure regulated oxygen to an oxygen header pipe  32 . The oxygen header pipe  32  has a plurality of flow meters  34  connected thereto and which are in fluid communication therewith to receive the pressure regulated oxygen vapor. The pressure regulator  28 , the first conduit  30 , the oxygen header pipe  32  and the plurality of flow meters  34  are all preferably disposed within the control panel  14 . The control panel  14  is preferably mounted to a fence, wall or other structure  35 . However, more or less items may be included in the control panel  14  and the control panel  14  can be located in a variety of other suitable locations. 
     The flow meters  34  (shown best in  FIG. 3 ) regulate the flow of oxygen from the header pipe  32  to a respective outlet conduit  36 . Each of the outlet conduits  36  is in communication with a respective one of a plurality of injection conduits  38 . While  FIG. 1  only shows a single outlet conduit  36 , it will be appreciated that each injection conduit  28  is directly connected to a separate outlet conduit  36 . Each of the injection conduits  46  terminates at a respective one of the plurality of injection sites or points  16 . Each of the injection sites preferably includes a screen attached at the end of each of the injection conduits  36 . Alternatively, the oxygen can be delivered into the groundwater through holes or slots formed in the end or sides of the conduits. 
     Accordingly, the number of flow meters  34  that are utilized in a particular system will depend upon the number of injection sites  16  that are determined to be necessary to clean up the groundwater at a given location. Similarly, the number of outlet conduits  36  and the number of injection conduits  38  will depend upon the number of injection sites  16  that are determined to be necessary to clean up a body of groundwater. Thus, each injection site  16  has an injection conduit  38 , an outlet conduit  36 , and a flow meter  34  associated therewith to regulate the flow of oxygen to that injection site  16 . The conduits, pipes, tubes, and injection points are preferably constructed of PVC piping. The outlet conduits  36  are preferably ¼-⅜ inch tubing and the injection conduits  30  are preferably ½ inch tubing. The size and material of the pipes and conduits can obviously vary. 
     As discussed above, in the preferred embodiment, a plurality of injection conduits  38  are utilized to convey the pure oxygen from the source of oxygen  12  to the injection sites  16 . While the source of oxygen  12  is preferably initially in liquid form, the pressure in the source  12  causes the liquid to turn to vapor. It is the pure oxygen vapor that is captured and then delivered through the delivery system and reacts with the microbials. The injection points  16  and the injection conduits  38  can be installed by any of a variety of methods, including by typical hollow stem auger with sand backfill. This is primarily for sites interbedded with clays and the like. Alternatively, the injection conduits  38  may be installed by known GeoProbe® (GeoProbe is a registered trademark of KEJR Engineering, Inc. of Kansas) installation techniques. 
     In accordance with the above-described system, the injection conduits  38  are preferably installed by airjet injection. Airjet injection is a novel installation technique that is part of the present invention. In accordance with the present invention, airjet injection utilizes a compressor that is connected to an injection conduit  38  via a hose or the like. The air flow and pressure from the compressor act as a cutting tool allowing the injection conduit  38  to be “injected” or inserted into the ground with minimal site description and with minimal time and capital expense. It has been determined that up to eighty (80) or more injection points can be installed in a single day. This is significantly higher than the number of points that could be installed under prior installation methods. 
     As shown in more detail in  FIG. 2 , each flow meter  34  is preferably connected to the oxygen header pipe  32  by a compression fitting  40  that allows oxygen at the regulated pressure to be delivered thereto. Each flow meter  32  is preferably mounted to a mounting board  42  or other structure in the control panel  14  and includes a pressure indicator  44  that provides a visual indication of the pressure of fluid, such as oxygen, flowing therethrough. The outlet conduits  36  that are in communication with the outlet of the flow meters  34  preferably extend through a protective conduit  46  (FIG.  1 ), which extends from the control panel  14  into the ground. The protective conduit  46  acts to shield and protect the outlet conduits  36  from damage. The outlet conduits  36  are preferably located at least one foot below the ground and run generally parallel thereto. The injection conduits  38  are in communication with a respective one of the outlet conduits  36  and extend generally perpendicularly downward from the respective outlet conduit  36  and into communication with the groundwater. As shown, the injection conduits  38  intersect the groundwater  18  below the water table at designated injection sites  16  in order to deliver the pure oxygen, and, if desired, microbials thereto. 
     Referring now to  FIG. 3 , which illustrates the desired chemical reaction induced in the groundwater by the preferred bioremediation system  10 . As shown, when a body of groundwater needs remediation, contaminants are present in the groundwater  18 , as generally indicated by reference number  48 . Oxygen molecules, as generally indicated by reference number  50 , are fed to a microbial, which is generally indicated by reference number  52 . The microbial  52  feeds off the oxygen molecules  50  and breaks down the contaminants  48  into a combination of water, as generally indicated by reference number  54  and carbon dioxide, as generally indicated by reference number  56 . It will be understood that the contaminants are typically a COC chain, but could be a variety of other contaminants that require removal. 
     Given that the above-described reaction can take a long time to remediate contaminants from groundwater naturally, it has been determined as part of the present invention, that pure or substantially pure oxygen works to clean up contaminants in a body of groundwater quicker and more efficiently than ambient air. Moreover, pure or substantially pure oxygen works to clean up contaminants more efficiently and at less cost than various oxygen releasing compounds. By increasing the amount of dissolved oxygen, it has been found that the bacterial population increases by over a magnitude of a thousand. One issue thus becomes how to deliver the pure oxygen into the ground and into communication with the groundwater. In accordance with the present invention, the preferred way is through the delivery system described above. Moreover, other delivery systems for conveying the oxygen to the injection sites may also be utilized. 
     The system  10  is preferably installed at a site that was formerly a service station (as shown in  FIG. 4 ) that has been determined to have groundwater, which is contaminated with petroleum, whether through accidental or intentional spillage. As is known, the groundwater can be tested through the use of a monitoring well to determine whether or not the groundwater has been contaminated. In accordance with the present invention, one way for determining the existence of contaminants is the absence or depletion of oxygen, which indicates that naturally existing bacteria are feeding on the oxygen in an effort to breakdown the contaminants. 
     When evaluating a site for feasibility of the disclosed system, it is best to start by looking at soil gas in the vadose zone just above the groundwater interface. Specifically, the concentrations of carbon dioxide and oxygen should be examined. When the soil gas in the area of groundwater contamination is examined, elevated levels of carbon dioxide and depleted or nearly depleted levels of oxygen are typically seen. When the soil gas outside the area of contamination is examined, it is typically found that the levels of carbon dioxide are lower than in the area of contamination and the levels of oxygen are higher than in the area of contamination. One must be careful in this comparison to assure a comparison of similar soil types and conditions. However, when this situation is identified it is reasonable to assume that the reason for the elevated level of carbon dioxide and depleted levels of oxygen within the contaminated zone is based on the presence of bacteria consuming all available oxygen and producing carbon dioxide. Because of the lack of oxygen in the contaminated area only a limited population of bacteria is possible, although all other conditions for a larger population exist. Any increase in the level of oxygen will increase the bacteria population and rate of contamination degradation. It can be assumed that a body of groundwater has unacceptable levels of contamination when the percentage of oxygen in soil gas in the vadose zone just above the groundwater interface, is less than approximately 21% oxygen and less than the oxygen levels in the vadose zone just above the groundwater interface, at nearby locations with similar soil conditions, that are known to be uncontaminated. 
     It can also be assumed that a body of groundwater has unacceptable levels of contamination when the percentage of carbon dioxide in soil gas in the vadose zone, just above the groundwater interface, is greater than 0.5 percent and greater than carbon dioxide levels in soil gas in the vadose zone just above the ground water interface at nearby locations with similar soil conditions that are known to be uncontaminated. 
     When these two situations occur simultaneously (that is, the depleted oxygen environment along the with elevated carbon dioxide environment), it is because there exists a population of bacteria consuming contamination along with available oxygen and respiring carbon dioxide. This assumption is further enhanced when at a location nearby with similar soil conditions, that is known to be uncontaminated, oxygen levels are significantly higher than at locations within the contaminated zone and carbon dioxide levels are significantly lower than at locations within the contaminated zone. One must be careful to assure comparisons of locations based proximity, similar soil types, and site conditions. 
     Once it has been determined that the groundwater is contaminated, in accordance with the present invention, the location of the injection points or sites can be determined. The location of the injection points can be determined in a variety of different methods. Preferably, however, the injection points are located in a grid that takes into account the direction and flow rate of groundwater flow. By taking into account the groundwater flow, as generally indicated by reference number  70 , injection sites will be positioned to prevent contaminants from spreading. Typical grid determination is based on site specifics, but generally, a grid is based on a determination of two months of groundwater flow (e.g. if the groundwater flows 120 feet per year, the grid would be a 20 foot grid). A grid pattern is preferred as it helps insure proper spacing between the injection sites  16 . A grid pattern is preferred as it helps insure proper spacing between the injection sites and consistent oxygen levels in the vadose zone—and in migrating groundwater 
     Accordingly, as shown in  FIG. 4 , the exemplary system  10  is installed at a gas station  60  having a plurality of dispenser islands  62 . The dispenser islands  62  were provided with petroleum from a plurality of storage tanks  64 . A plurality of monitoring wells  58  are utilized to determine the extent and location of any contaminants so that the system usage can be maximized. In  FIG. 4 , five (5) monitoring wells  58  are illustrated. Obviously, any number of monitoring wells can be included. The injection sites  16  are preferably located in a grid pattern as shown (i.e. columns and rows), and then the injection conduits  38 , which are connected to the source of oxygen  12  and the control panel  14  are installed to inject oxygen into the groundwater at the injection sites  16 . As set forth above, the injected oxygen is preferably pure, but need only have sufficient purity to accomplish the objects of the invention are achieved. 
     Once the system  10  is installed, the oxygen vapor is regulated and metered to be delivered into the groundwater at a predetermined rate. The rate is preferably adjusted over time. The dissolved oxygen in the groundwater and the amount of oxygen in the soil gas vapor is monitored to assure a sufficient flow of oxygen to the injection sites  16 . Similarly, the oxygen is monitored to determine if too much oxygen is being added in order to prevent undue waste of oxygen and thereby increase expense. In accordance with the present invention, it has been determined through testing that the preferred level of oxygen present in soil gas vapor is in the range of about approximately 15% to 25%. More preferably, the level of oxygen in the soil gas vapor is approximately 21%. It will be understood that the level of oxygen in the soil gas vapor can vary. For example, it can be higher than 25%, even though it is believed that levels above 25% can be inefficient. Moreover, it can also be lower than 15% depending upon the application. The level of oxygen in the soil gas vapor can be determined through soil gas monitoring and testing techniques, as are known in the art. 
     The level of oxygen in the soil gas can be controlled by regulating the flow of oxygen to each of the injection sites  16  through their associated flow meters  34 . If not enough oxygen is injected into the groundwater, i.e., the level of oxygen in the soil gas vapor is significantly less than 15%, the remediation process will not occur any faster than it would naturally. If too much oxygen is injected into the groundwater, the remediation process will not occur any faster than it would with the preferred levels of oxygen. Obviously, the flow rate and pressure of the oxygen vapor to the injection sites  16  can be varied as needed to increase or decrease the flow rate of oxygen. The effect of the system on the contaminants can be monitored periodically through the monitoring wells. Further, if the source of oxygen  12  becomes depleted, it can be easily replaced without disrupting the clean up process. 
     The preferred system is relatively inexpensive to install as it costs significantly less than prior systems. Moreover, the system operates twenty-four hours a day and requires no electricity or maintenance to operate. Further, as there are no moving parts, there is nothing to lube, oil or grease. The system is also less susceptible to break down. 
     While particular embodiments of the invention have been shown and described, numerous variations and alternate embodiments will occur to those skilled in the art. Accordingly, it is intended that the invention be limited only in terms of the appended claims.