Abstract:
The present invention includes methods and a system for treating a mass of contaminated media using ammonia. The methods include determining the amount of ammonia required for treatment using various calculation methods and combining the ammonia with air or another carrier gas to create a gas mixture. The methods and system utilize at least one injection well inserted into the contaminated media to deliver the gas mixture over a period ranging from approximately 1 week to approximately 8 weeks.

Description:
STATEMENT OF GOVERNMENT INTEREST 
     The invention was supported, in part, by funding from the Department of Defense Environmental Security Technology Certification Program (ESTCP), and from the Environmental Protection Agency (EPA). The United States Government has certain rights in the invention. 
    
    
     BACKGROUND 
     1. Field of Invention 
     This invention relates to the field of hydraulic and earth engineering, and more specifically to in situ contaminant removal or stabilization. 
     2. Detailed Description of Prior Art 
     Alkaline hydrolysis is a process for treatment of contaminated soil that involves raising pH levels to cause the contaminant to break down. This process has been successfully used for contaminants located primarily relatively close to the surface. However, alkaline hydrolysis has been unsuitable for treating contaminants trapped at intermediate and deeper levels of soil. 
     Liquid chemical applications, designed to penetrate the subsurface, flow downward through narrow cracks, crevices, and high-permeability channels present in soil. The liquid chemical becomes concentrated in some areas and bypasses large portions of the soil in others. High concentrations of alkaline materials may render drinking water unsafe and cause injury or damage to humans, animals and crops. 
     There is an unmet need in the art for a controlled method of alkaline hydrolysis that is effective for eradicating subsurface soil contamination without causing additional environmental damage. 
     SUMMARY OF THE INVENTION 
     In one embodiment of the invention, a method for treating a mass of contaminated media includes the steps of removing a sample of the contaminated media and testing the sample to determine a current pH level P A  and a current lime buffering capacity B L  of the contaminated media, then calculating a quantity M of the ammonia needed for treatment of the contaminated media using the equation
 
 M =( P   D   −P   A )* A   C   *F*B   L  
 
wherein P D  is a desired pH of the contaminated media, A C  is a constant value of approximately 0.34 milligrams of the ammonia per milligram of calcium carbonate, F is a safety factor of approximately 10.4. The method then inserts the at least one injection well into the contaminated media at the distribution, creates a gas mixture by combining the quantity M of the ammonia with air and delivers the gas mixture over a period ranging from approximately 1 week to approximately 8 weeks.
 
     In another embodiment of the invention, a method for treating a mass of contaminated media includes the steps of removing a sample of the contaminated media, administering a known quantity M T  of ammonia to the sample of the contaminated media by injecting the known quantity of ammonia through the sample of the contaminated media, testing the sample of the contaminated media to determine a current pH P A  of the sample of the contaminated media and calculating a quantity of ammonia M needed for treatment of the contaminated media using the equation 
             M   =         M   T     *     M   C     *     (       P   D     -     P   A       )           M   S     *     (       P   D     -     P   A       )               
wherein M C  is a mass of the contaminated media to be treated, P D  is a desired pH of the contaminated media, and M S  is a mass of the sample of contaminated media. The method then inserts the at least one injection well into the contaminated media, creates a gas mixture of the ammonia with air and/or a carrier gas and delivers the gas mixture over a period ranging from approximately 1 week to approximately 8 weeks.
 
     In another embodiment of the invention, a system for treating contaminated media includes an air source, an ammonia source, at least one injection well and a control cabinet. The air source contains air. The ammonia source contains a quantity M of the ammonia required to treat the contaminated media, the quantity M calculated using the equation
 
 M =( P   D   −P   A )* A   C   *F*B   L  
 
wherein P D  is the desired pH of the contaminated media, P A  is the current pH of the contaminated media, A C  is a constant value of approximately 0.34 milligrams of the ammonia per milligram of calcium carbonate, F is a safety factor of approximately 10.4 and B L  is a lime buffering capacity of the contaminated media expressed in units of milligrams of calcium carbonate per kilogram of the contaminated media per unit of pH. The control cabinet is connected between the air source, the ammonia source and the at least one injection well.
 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  illustrates an exemplary system for raising the pH of contaminated media to promote in situ alkaline hydrolysis of contaminated media. 
         FIGS. 2 a  and 2 b    illustrate a flowchart of an exemplary method for raising the pH of contaminated media to promote alkaline hydrolysis reactions. 
     
    
    
     TERMS OF ART 
     As used herein, the term “groundwater” means water occurring below the ground surface. 
     As used herein, the term “lime buffer capacity” means the amount of media acidity that must be neutralized to raise media pH by one unit, expressed in units of milligrams of calcium carbonate per kilogram of media per unit of pH. 
     As used herein, the term “perched water” means groundwater occurring in a saturated zone separated from a main body of groundwater by unsaturated rock, sediments or soil. 
     As used herein, the term “saturated” or “saturation” means a state wherein additional water cannot be absorbed. 
     As used herein, the term “vadose zone” means a zone of soil extending from the ground surface to the water table. 
     DETAILED DESCRIPTION OF INVENTION 
       FIG. 1  illustrates an exemplary system  100  for promoting in situ alkaline hydrolysis of contaminated media S. System  100  includes an air source  10  providing air  11 , an optional carrier gas source  20  providing an optional carrier gas  21 , an ammonia source  30  providing ammonia  31  to create a gas mixture  35 , an injection well  40 , an optional blower  50  and a control cabinet  60 . 
     Air source  10  provides air  11 . Air  11  conveys carrier gas  21 , ammonia  31  and other gases in gas mixture  35  to injection well  40 . In the exemplary embodiment, air source  11  is a compressor and compressed air tank. In another embodiment, blower  50  propels air  11  through system  100 . 
     Optional carrier gas source  20  contains a carrier gas  21  including, but not limited to, nitrogen or other gasses. Carrier gas source  20  supplies carrier gas  21  as compressed gas or refrigerated liquid, or through generation membrane or pressure swing adsorption processes. Carrier gas  21  provides an additional or alternate gas to combine with ammonia  31  to create gas mixture  35  if air  11  contains unacceptable levels of oxygen or other components that could create an explosion hazard or dangerous conditions. 
     Ammonia source  30  for ammonia  31  may be a tank of liquid anhydrous ammonia, or a tank of compressed gaseous ammonia. In one embodiment, in gas mixture  35  combining ammonia  31  with air  11  and/or carrier gas  21 , ammonia  31  makes up approximately 4% to approximately 14% of gas mixture  35 . In another embodiment, ammonia  31  concentrations ranging from approximately 15% to approximately 28% may be used if carrier gas  21  is substituted for air  11 , to mitigate the risk of creating an explosive gas mixture. In another embodiment, in gas mixture  35  combining ammonia  31  with air  11  and/or carrier gas  21 , ammonia  31  makes up more than approximately 28% of gas mixture  35 . The concentration of this embodiment may be used if there are barriers, geological features, or climactic conditions which mitigate the risk of ammonia  31  (or transformation products) migrating to groundwater. 
     Injection well  40  is a hollow tubular insert approximately 1 inch to 4 inches in diameter, constructed from polymers, metals or other rigid materials. Injection well  40  extends from the surface of contaminated media S to a given treatment depth to allow delivery of gas mixture  35 , and may extend through multiple different types of contaminated media S, such as both soil and groundwater. One embodiment utilizes a single injection well  40 , while other embodiments include multiple injection wells  40 . In embodiments using multiple injection wells  40 , the distribution of injection wells  40  depends on a pneumatic permeability K of contaminated media S. 
     Injection well  40  has solid sidewalls except for at least one perforated section  41 . Perforated section  41  includes apertures that allow delivery of gas mixture  35  from injection well  40  into contaminated media S. If contaminated media is located in a multiple subsurface layers, then injection well  40  may include more than one perforated section  41 . For example, if contaminated media S were located at depths of 10-12 feet and 20-24 feet, then injection well  40  would include first and second perforated sections  41 . A first perforated section  41  would begin at a location 10 feet from a first end and extend 2 feet along injection well  40 . A second perforated section  41  would begin at a location 20 feet from an upper end and extend 4 feet along injection well  40 . 
     In one embodiment, injection well  40  also includes a surface cover  42 . Surface cover  42  is impermeable to gas and prevents any delivered gas mixture  35  from escaping up through contaminated media S and into the atmosphere, particularly during delivery at a shallow depth. 
     In one embodiment, injection well  40  also includes at least one resistive heating element  43  located on an outer surface of injection well  40 . Resistive heating element  43  allows heating of contaminated media S to temperatures ranging from approximately 20 degrees Celsius to approximately 70 degrees Celsius. Because ammonia  31  is hydrophilic, and has a very high solubility in water, the water content of contaminated media S influences the radial distribution of ammonia  31  from injection well  40 . Increasing water content reduces the radial distribution of ammonia  31 . Heating contaminated media S can decrease its water content. 
     Blower  50  may be used to convey gas mixture  35  to injection well  40 . Blower  50  propels air  11  through system  100 , allowing air  11  to convey carrier gas  21 , ammonia  31  and other gases of gas mixture  35  to injection well  40 . Due to this function, blower  50  must be located “upstream” of carrier gas source  20  and ammonia source  30 , or of a piping junction where carrier gas source  21  and ammonia source  31  are introduced. In certain embodiments, blower  50  also heats air  11 . 
     Control cabinet  60  incorporates at least one flow meter  61  and a static mixer  62 . Flow meter  61  allows a user to regulate the flow of air  11 , carrier gas  21 , ammonia  31  and other gases to ensure gradual delivery of gas mixture  35 . Static mixer  62  evenly combines air  11 , carrier gas  21  and ammonia  31  to create gas mixture  35 . 
       FIGS. 2 a  and 2 b    illustrate an exemplary method  200  for raising the pH of contaminated media S to promote alkaline hydrolysis reactions. Method  200  raises the pH of contaminated media S such as soils, groundwater, perched water and sediments. In one embodiment, contaminated media S is unsaturated soil. In another embodiment, contaminated media S is soil in the vadose zone. In alternate embodiments, the contaminated media S is saturated soils and sediments. 
     In steps  202  to  206 , method  200  determines a quantity M of ammonia  21  required to raise the pH of contaminated media S. 
     In step  202 , method  200  removes a sample of contaminated media. 
     In step  204 , method  200  tests the sample of contaminated media S to determine current pH P A  and lime buffering capacity B L . 
     In step  206 , method  200  calculates quantity M of ammonia  21  needed using the equation
 
 M =( P   D   −P   A )* A   C   *F*B   L  
 
wherein P D  is the desired pH of contaminated media S, A C  is a constant value of approximately 0.34 milligrams of ammonia per milligram of calcium carbonate and F is a safety factor of approximately 10.4.
 
     In steps  208  to  214 , method  200  determines quantity M of ammonia  21  required to raise the pH of contaminated media S using an alternate method. 
     In step  208 , method  200  removes a sample of contaminated media S. In one embodiment, the sample of contaminated media S is removed to a test column. 
     In step  210 , method  200  administers a known quantity M T  of ammonia  21  to the sample of contaminated media S by injecting known quantity M T  of ammonia  21  into the sample of contaminated media S. In one embodiment, injection is performed through the test column at a known flow rate and temperature. 
     In step  212 , method  200  tests the sample of contaminated media S to determine current pH P A  after treatment. 
     In step  214 , method  200  calculates the quantity M of ammonia  21  needed for treatment using the equation 
             M   =         M   T     *     M   C     *     (       P   D     -     P   A       )           M   S     *     (       P   D     -     P   A       )               
wherein M C  is the mass of contaminated media S and M S  is the mass of the sample of contaminated media S.
 
     In optional step  216 , when method  200  utilizes a plurality of injection wells  40 , method  200  selects the distribution of injection wells  40  based on pneumatic permeability K of contaminated media S, calculated using the equation 
     
       
         
           
             K 
             = 
             
               
                 
                   Q 
                   * 
                   
                     P 
                     * 
                   
                   * 
                   μ 
                 
                 
                   π 
                   * 
                   b 
                 
               
               ⁢ 
               
                 
                   ln 
                   ⁡ 
                   
                     ( 
                     
                       
                         r 
                         2 
                       
                       / 
                       
                         r 
                         1 
                       
                     
                     ) 
                   
                 
                 
                   
                     P 
                     1 
                     2 
                   
                   - 
                   
                     P 
                     2 
                     2 
                   
                 
               
             
           
         
       
     
     wherein Q is the volumetric flow rate, P* is the pressure at the point of flow measurement, p is the viscosity of air, b is the vertical thickness of contaminated media S, r 1  and r 2  are the distance to observation points and P 1  and P 2  are the absolute pressures at observation points. 
     In optional step  218 , method  200  modifies the structure of contaminated media S to allow insertion of at least one injection well  40  into contaminated media S as determined in step  216 . In one embodiment, method  200  removes a portion of contaminated media S to form a void in the contaminated media sized to accept injection well  40 . This removal can utilize hand tools, an auger drill or other power tools. The void will have a diameter at least as large as the outer diameter of injection well  40  and a depth sufficient to align perforated section  41  with the full thickness of contaminated media S. 
     In step  220 , method  200  inserts at least one injection well  40  into contaminated media S at intervals determined in step  216 . 
     In optional step  222 , method  200  performs hydraulic or pneumatic fracturing to increase the permeability of contaminated media S. 
     In optional step  224 , method  200  may increase the temperature of contaminated media S. In one embodiment, this step delivers heated gas, such as steam or heated air  11 , to contaminated media S through injection well  40 . In another embodiment, the user runs electric current through at least one resistive heating element  43  located on an outer surface of injection well  40 . The final temperature of contaminated media S ranges from approximately 20 degrees Celsius to approximately 70 degrees Celsius. 
     In optional step  226 , method  200  may increase the moisture content of contaminated media S. This step delivers humidified gas, such as steam, or air  11  or carrier gas  21  humidified by passage through water spray or by bubbling through a water vessel. The final moisture content of contaminated media S may range from approximately 5% to any point below media saturation. 
     In step  228 , method  200  creates gas mixture  35  by combining ammonia  31  with air  11  and/or carrier gas  21 . Depending on the embodiment, ammonia  21  makes up approximately 4% to approximately 14%, approximately 14% to approximately 28% or more than approximately 28% of gas mixture  35 . 
     In step  230 , method  200  delivers gas mixture  35 . Delivery may occur over a period ranging from approximately 1 week to approximately 8 weeks. In certain embodiments, step  230  may be performed simultaneously with step  224  and/or step  226 . 
     In optional step  232 , method  200  waits for a period of approximately 2 weeks to approximately 6 weeks for completion of any chemical reactions in contaminated media S. 
     In optional step  234 , method  200  retests for pH levels. 
     In optional step  236 , method  200  tests for contaminant levels. 
     In optional step  238 , method  200  performs step  224  to heat contaminated media S and/or reduce the moisture content in contaminated media S. In certain embodiments of method  200 , treatment of a large area may follow treatment of a small area. Heating contaminated media S allows this sequence using the same distribution of injection wells  40 . 
     In optional step  240 , method  200  performs step  226  to increase the moisture content in contaminated media S. In certain embodiments of method  200 , treatment of a small area may follow treatment of a large area. Increasing the moisture content of contaminated media S allows this sequence using the same distribution of injection wells  40 . 
     In optional step  242 , method  200  repeats performance of steps  206 ,  228  and  230 . In certain embodiments of method  200 , treatment of contaminated media S may be separated into multiple iterative treatments using smaller amounts of ammonia  31  to allow more precise control over the process or to prevent the build-up of dangerous chemicals, such as nitrates. 
     In optional step  244 , method  200  removes injection well  40 . If method  200  does not remove injection well  40 , then injection well  40  remains in place and is abandoned. 
     It will be understood that many additional changes in the details, materials, procedures and arrangement of parts, which have been herein described and illustrated to explain the nature of the invention, may be made by those skilled in the art within the principle and scope of the invention as expressed in the appended claims. 
     It should be further understood that the drawings are not necessarily to scale. Instead, emphasis has been placed upon illustrating the principles of the invention. Like reference numerals in the various drawings refer to identical or nearly identical structural elements. Moreover, the term “approximately” as used herein may be applied to modify any quantitative representation that could permissibly vary without resulting in a change in the basic function to which it is related. Furthermore, all percentages referred to herein are percentages by volume.