Abstract:
In the present invention, a plurality of conduits are employed for introducing Fenton&#39;s reagent reaction components separately into a site for treating a target contaminant. The conduits are disposed in a subsurface borehole which can be positioned, prepared and sealed as in the prior art. At the surface-accessible end of each conduit, an injection head is provided. At the subsurface end of each conduit, various means are provided for allowing the components to contact one another to form Fenton&#39;s reagent and for delivering the reagent to the contamination site.

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS  
       [0001]    This application claims the benefit of U.S. provisional application 60/183,947, filed on Feb. 22, 2000, which is incorporated herein in its entirety. 
     
    
     
       STATEMENT REGARDING FEDERALLY SPONSORED RESEARCH OR DEVELOPMENT  
         [0002]    Not applicable.  
         BACKGROUND OF THE INVENTION  
         [0003]    Representative examples of devices and methods for remediating, e.g., DNAPLs and LNAPLs in soil and groundwater that use Fenton&#39;s reagent include U.S. Pat. Nos. 5,520,483; 5,525,008; 5,611,642; 5,741,427; and 5,286,141, each incorporated herein by reference as if set forth in its entirety. The incorporated patents disclose principles of treating subsurface contamination, including how and where to place boreholes to ensure treatment of subsurface contamination. Such principles are considered to be well within the level of ordinary skill in the art and are not further detailed herein.  
           [0004]    In all known in situ remediation methods that utilize Fenton&#39;s reagent, the reaction components (namely, hydrogen peroxide and iron sulfate catalyst) are either (1) added sequentially so that mixing occurs in the site or (2) are mixed prior to being introduced into the subsurface (subterranean) remediation site. Each of these methods has significant shortcomings. The former method depends on the normal diffusive characteristics of the remediation site to mix separately introduced reaction components in the soil and groundwater and thus is inefficient, time consuming and expensive. This method can also be hazardous as an explosively high concentration of hydrogen peroxide can accumulate near the well if the reaction components are inefficiently dispersed. The latter method is also inefficient in that the components disadvantageously react with each other before having an opportunity to productively react with the contaminant in the lithology. Moreover, when the components are mixed together in the latter method, they become violently reactive and can explode while being delivered to the remediation site.  
           [0005]    Thus an apparatus and methods for in situ remediation using Fenton&#39;s reagent that overcome the known disadvantages of existing remediation systems are desired.  
         BRIEF SUMMARY OF THE INVENTION  
         [0006]    The present invention is summarized in that a method for subsurface in situ remediation (or decrease in concentration of a contaminant) using Fenton&#39;s reagent includes the steps of separately delivering each component of Fenton&#39;s reagent in a conduit to a site to be remediated, wherein the components do not mix with one another until both components reach the remediation site.  
           [0007]    The present invention is further summarized in that an apparatus suited for practice of the method comprises at least one pair of conduits for introducing and mixing Fenton&#39;s reagent reaction components in a subsurface borehole which can be provided and positioned near a target contaminant as in the prior art. Each conduit has a subsurface end and a surface-accessible end provided outside of a seal that isolates the apparatus from the surface environment. An injection head is provided at the surface-accessible end of each conduit. At the subsurface end of each conduit, means are provided for combining the reaction components that are separately introduced into the borehole. In a first embodiment, the conduits fluidly communicate directly with an outlet in which the reaction components mix and through which the mixed reaction components enter the remediation site. In a related embodiment, both subsurface conduit ends comprise an outlet and the pair of outlets are provided in a larger outlet that is less permeable and has a slower outflow rate than the outlets attached to the conduits, such that adequate mixing of reaction components can occur inside the larger outlet before the mixed components are delivered to the remediation site. In yet another embodiment, the channels can fluidly communicate with a coupling wherein the components are mixed before exiting the apparatus via the outlet. In still another embodiment, a first conduit for delivering a first reaction component resides inside a second conduit used for delivering a second reaction component. In all embodiments, the reaction components delivered by the two conduits do not mix before reaching the subsurface ends of the conduits, which are in fluid communication with a mixing coupling and outlet, or directly with an outlet.  
           [0008]    It is an object of the present invention to mix the reaction components just before being introduced to a remediation site.  
           [0009]    It is an advantage of the present invention that efficiency benefits are realized in the Fenton&#39;s reaction because the components mix just before being introduced into a remediation site, as opposed to the devices and methods of the prior art wherein undesired and sometimes violent reaction can occur in the injection head and/or in the conduit when the components are introduced sequentially.  
           [0010]    It is another advantage of the present invention that the injection heads can be moved from one location to another quickly and safely since the reactive components do not mix and do not react at the injection head end of the conduits.  
           [0011]    Further objects, features and advantages of the invention will be apparent from the following detailed description when taken in conjunction with the accompanying claims and drawings. 
       
    
    
     BRIEF DESCRIPTION OF THE SEVERAL VIEWS OF THE DRAWINGS  
       [0012]    [0012]FIG. 1 depicts an embodiment of the two conduit injection system of the present invention.  
         [0013]    [0013]FIG. 2 depicts an alternate embodiment of the two conduit system.  
         [0014]    [0014]FIG. 3 details the assembly of the embodiment of FIG. 2.  
         [0015]    [0015]FIG. 4 depicts another alternate embodiment of the two conduit system.  
         [0016]    [0016]FIG. 5 depicts use of multiple two conduit systems for remediating a site at various depths. 
     
    
     DETAILED DESCRIPTION OF THE INVENTION  
       [0017]    One embodiment of the present invention is shown in FIG. 1. A plurality, at least a pair, of separate non-corrosive pipes  12 ,  13  of similar diameter, each having a surface-accessible (upper) end and a subsurface (lower) end are provided in a conventional borehole  11  at a suitable depth. Procedures for making boreholes are well known to one of ordinary skill in the art. For example, a hollow-bore auger can be used to dig the hole and the pipe assembly can be placed in the hole through the hollow space in the middle of the auger. The borehole that accommodates the apparatus can be made and filled in accord with convention in the art.  
         [0018]    The surface-accessible end of each pipe is coupled to an injection head  21  through which a reaction component can be provided. The subsurface end of each pipe is coupled with a substantially fluid-tight seal to a non-corrosive mixing coupling  14  having an upper surface that defines openings for fluid communication with the pipes  12 ,  13 . The mixing coupling  14  of FIG. 1 can define a chamber of in any shape and can have no internal structure (a “static mixer”) for promoting mixing of the reagents. It can, on the other hand, contain fluid-disturbing structures for encouraging mixing of the reaction components. Examples of such structures include blades or flaps  17  (as shown in FIG. 1) extended from the interior walls and a funnel arrangement in the mixing coupling&#39;s interior beneath the pipes.  
         [0019]    The mixing coupling  14  also has a lower surface that defines at least one opening for substantially fluid-tight connection to an outlet in fluid communication with the coupling  14  for receiving mixed reactants. The outlet is permeable such that the mixed components in the outlet exit the apparatus into the lithology while preventing foreign matter from entering the apparatus. In the embodiment of FIG. 1, the outlet is a conventional well screen  15  that can be made of stainless steel or other material that is sufficiently non-corrosive to endure the subsurface environment in which the apparatus finds application. For example, the well screen can be a hollow plastic cylinder made of PVC having holes of appropriate size therethrough on the cylinder walls. The screen can also be a stainless steel coil with appropriate spaces in between.  
         [0020]    A skilled artisan understands the attributes of the injection heads coupled to each pipe  12 ,  13  at the surface-accessible end. On the injection heads  21 , valves such as a pressure relieve valve  24 , check valves  25  and ball valves  26 , gauges such as a pressure gauge  28 , and couplings such as quick-connect couplings  29  of a type known in the art facilitate operation. In a preferred embodiment, each injector head comprises a pair of inputs  55  and  56  for feeding the reaction components into the pipes as shown in FIG. 1 where one of inputs  55  and  56  is coupled to a reaction component (shown schematically at  22 ) and the second input is coupled to a source of compressed air (shown schematically at  23 ) for urging the reaction component  22  into the pipe. While the injection head inputs  55  and  56  are provided on a single side of the pipe in FIG. 1, they can also be located on opposite sides in a T- or substantially T-shaped structure. Releasable coupling means, such as threaded ends, can be provided at the surface-accessible end of the on the pipes  12 ,  13 , if removable injection heads are contemplated.  
         [0021]    The apparatus can be sealed in the borehole as in conventional one pipe systems. The mixing coupling  14  and the well screen  15  can be surrounded and stabilized by particulate material  16 , such as sand, preferably silica sand having a particle size sufficiently large that it is substantially prevented from entering the well screen  15 . The pipes can be stabilized in the borehole with grout  18  with an optional layer of bentonite  19  or other clay material therebetween. When a hollow bore auger is used, sand  16 , bentonite  19  and grout  18  can be place in the borehole while the auger is being retrieved after the pipe assembly has been placed in the borehole.  
         [0022]    In use, an iron sulfate reaction catalyst is added via a first injection head to a first conduit and hydrogen peroxide is added via a second injection head to a second conduit. The Fenton&#39;s reagent reaction components do not mix during delivery in the conduits to the treatment site, but rather mix after the components have left the conduits, optionally in the mixing coupling, before exiting from the apparatus outlet into the treatment site.  
         [0023]    [0023]FIG. 2 depicts an related embodiment wherein no mixing coupling is provided and the lower end of each pipe  12 ,  13  is connected to its own well screen  41 . The well screens, in turn, are disposed inside a larger well screen  42  that is less permeable and has a slower outflow rate than those attached to the pipes, such that adequate mixing of reaction components can occur inside the larger well screen before the mixed components are delivered to the remediation site. FIG. 3 shows how the pipes  12 ,  13 , the small screens  41  and the large screen  42  are assembled together using connector  51 . Connector  51  defines at least a pair of female threaded  52  channels therethrough and is further provided with a male thread on an outer surface. Each female threaded channel receives from one side of the connector  51  a pipe  12  or  13  and from the other side of the connector  51  a well screen  41 . Larger well screen  42  is threaded to the connector  51  at  55 . In this embodiment, a back flow preventer  43  can be used with each pipe near the lower end of the pipe.  
         [0024]    In another arrangement, as shown in FIG. 4, the pipes are not separate and do not have similar or identical diameters. This arrangement employs a pipe  31  having an inside wall and an inner diameter sufficiently large to accommodate a smaller inner pipe  32 . Inner pipe  32  has an outer wall and an outer diameter smaller than the inner diameter of pipe  31 . Channel  33  is defined by the inside wall of pipe  31  and the outside wall of pipe  32 . Channel  34  is defined by the inside wall of inner pipe  32 . A mixing coupling can also be provided to connect the pipes and the screen in this embodiment. The components are delivered separately to the subsurface via the channels  33 ,  34  and do not mix until they reach screen  15 , which is connected to pipe  31 , as shown in FIG. 4.  
         [0025]    Depending on whether the contaminants to be remediated are, e.g., DNAPLs (dense non-aqueous phase liquids) or LNAPLs (light non-aqueous phase liquids), the contamination may be found at different depths from the ground surface. LNAPLs such as gasoline are typically found closer to the surface than DNAPLs such as chlorinated solvents TCE and PCE. It will be understood that multiple two-pipe systems of the types disclosed can be positioned at distinct depths by varying the pipe lengths to remediate contaminants located at various distances below the surface (shown in FIG. 5).  
         [0026]    The apparatus has been successfully used for in situ subsurface remediation to decrease the amount and concentration of both subsurface DNAPLs and LNAPLs using Fenton&#39;s reagent prepared in accordance with the method of the invention.  
         [0027]    It is understood that the particular embodiments set forth herein are illustrative and not intended to confine the invention, but embraces all such modified forms thereof as come within the scope of the following claims.