Abstract:
This invention is directed to a process for treating the flow of anaerobic groundwater through an aquifer with a primary treatment media, preferably iron, and then passing the treated groundwater through a second porous media though which an oxygenated gas is passed in order to oxygenate the dissolved primary treatment material and convert it into an insoluble material thereby removing the dissolved primary treatment material from the groundwater.

Description:
STATEMENT AS TO RIGHTS TO INVENTIONS MADE UNDER FEDERALLY SPONSORED RESEARCH AND DEVELOPMENT 
     The Government has rights in this invention under contract. 
    
    
     BACKGROUND OF THE INVENTION 
     1. Field of the Invention 
     This invention relates to the removal of iron and manganese from groundwater. More particularly, this invention relates to the removal of iron and manganese released from the treatment media of a primary in-situ groundwater treatment system. 
     2. Description of Related Art 
     Groundwater in many localities has become contaminated by both natural and manmade impurities. Due to the considerable reliance on groundwater as a primary source of potable water, treatment of polluted groundwater to remove such contaminants has gained significant interest within the last decade. Many treatment systems for the removal of groundwater contaminants have been proposed, including pump-and-treat systems, well injection of treatment agents, and in-situ treatment. Due to the significant cost savings, in-situ treatment of groundwater has drawn considerable interest in recent years. In-situ treatment of groundwater is discussed in  NEW APPROACH TO IN - SITU TREATMENT OF CONTAMINATED GROUNDWATERS;  McMurty et at.,  Environmental Progress  1985. 
     McMurtry discusses the use of permeable barrier walls placed in trenches excavated into native aquifers to treat contaminated groundwater. The permeable barrier contains appropriate treatment media, such that the quality of the contaminated groundwater flowing through the media is significantly improved. McMurtry states that most in-situ groundwater treatments will be in isothermal, anaerobic, reducing environments. Many in-situ groundwater treatment systems take advantage of this anaerobic, reducing environment, in conjunction with the selected treatment material to remove or transform the chemical contaminants in the groundwater into nonhazardous material. Typically treatment materials are limestone, activated carbon, active metals, or biological agents. These in-situ treatment systems, while removing or neutralizing many dangerous contaminants, may add other manmade contaminants to the groundwater. For example, a common treatment material for in-situ treatment is elemental or zero valent iron. While removing many contaminants, elemental iron adds iron and other metallic impurities (e.g., manganese) to the groundwater. Removal or neutralization of these manmade impurities from groundwater is essential in returning groundwater in a native aquifer to a useable state. 
     BRIEF SUMMARY OF THE INVENTION 
     An object of this invention is to provide a method to remove iron and manganese impurities present in groundwater due to a primary in-situ groundwater treatment material. 
     This and other objectives of the invention, which will become apparent from the following description, have been achieved by a novel improvement to in-situ groundwater treatment systems to remove secondary sources of groundwater contamination released by the treatment media from primary in-situ treatment systems into native aquifers. The primary in-situ treatment system, for use with the treatment system of this invention, relies on the flow of groundwater, through an aquifer, into the primary treatment system to decontaminate the groundwater through the use of a metallic treatment material. The primary treatment system may add metallic-based contaminants while decontaminating the groundwater. The improvement of this invention is to oxygenate the oxygen-deficient groundwater after in-situ treatment by the metallic treatment material in order to remove the metallic-based contaminants added to groundwater by the primary in-situ treatment system. The treatment system of this invention is particularly useful when the groundwater is maintained in an anaerobic condition, and the primary treatment system and media is maintained under anaerobic conditions. 
     The primary in-situ groundwater treatment process includes determining the conditions of the groundwater in the aquifer and the contaminate; selecting and placing the primary metallic-based treatment material into the aquifer; directing the flow of the anaerobic groundwater through the primary treatment material to neutralize the contaminant while maintaining the groundwater under an anaerobic environment and permitting the treated groundwater to reenter the aquifer. During the course of treatment, a portion of the metallic-based primary treatment agent becomes soluble in the groundwater. The process of the invention relates to the oxygenation of the anaerobic groundwater by permitting it to pass through a second treatment material that provides a source of oxygen, thereby converting the solublized metal-based treatment media into insoluble metallic oxides. Preferably, the process of this invention oxygenates the oxygen deficient groundwater contaminated by metallic-based impurities from the primary treatment source by passing the contaminated groundwater through porous treatment media through which a flow of oxygenated gas is directed. 
     More specifically, the primary in-situ groundwater treatment process comprises, determining the direction, volume and velocity of a region of contaminated material dissolved within a stream of groundwater flowing through an aquifer. A metallic-based primary treatment material is provided. A primary repository is formed within the aquifer for containing a primary treatment material. The primary treatment material is placed in the primary repository such that the primary treatment material lies in the path of the region of contaminated material. The primary repository is oriented such that the region of contaminated material enters the primary repository through the upstream side thereof. The placement of the repository being such that the flow of the groundwater in the aquifer in which the primary repository is located causes the region of contaminated material to pass from the aquifer into the primary repository, pass through the treatment media within the primary repository, and exit from the downstream side of the primary repository. The permeability of the primary treatment material being such that the resistance to the passage of groundwater through the primary repository is substantially no greater that the resistance of the native aquifer to the passage of groundwater through the aquifer. The primary treatment material causes the dissolved contaminated material to be rendered inactive in the groundwater. During the course of the primary treatment, a portion of the primary treatment media dissolves in the stream of groundwater flowing through the primary repository, exits in the groundwater flowing therethrough, and enters into the native aquifer. 
     The improvement, as outlined hereinabove comprises: forming a secondary repository within the aquifer downstream of the first repository for containing a porous media. A source of oxygenating gas is placed adjacent to the base of the repository. Porous media is installed above the source of oxygenating gas such that the porous media lies in the path of the flow of dissolved primary treatment material. The orientation of the secondary repository is such that the flow of dissolved metallic-based contaminants from the primary treatment material enters the second repository through the upstream side thereof. The placement of the secondary repository being such that the flow of the groundwater in the aquifer in which the second repository is located causes the flow of dissolved primary treatment material to pass from the aquifer into the second repository, pass through the second repository from side to side thereof, and exit from the downstream side of the second repository. The permeability of porous media is such that the resistance to the passage of groundwater through the second repository is substantially no greater that the resistance of the native aquifer to the passage of groundwater through the aquifer. The oxygenating gas is directed up though porous medium such that the flow of groundwater containing the dissolved contaminants, based on the primary treatment material, in the groundwater is oxygenated thereby making the dissolved primary treatment material insoluble. 
     The process is of particular utility when the primary treatment material contains elemental iron or manganese. Further, the process of this invention is most beneficial when the dissolved iron in the groundwater from the primary treatment material is made into insoluble oxides. 
    
    
     BRIEF DESCRIPTION OF THE SEVERAL VIEWS OF DRAWINGS 
     With this description of the invention, a detailed description follows with reference being made to the accompanying figures of drawings which form part of the specification, in which like parts are designated by the same reference numbers, and of which: 
     FIG. 1 is a cross-sectional view illustrating the treatment system of this invention; 
     FIG. 2 is an enlargement of the top cross-sectional view illustrating the aeration system for use with this invention; 
     FIG. 3 is an alternative arrangement of the instant invention wherein the primary treatment system is tank-based. 
    
    
     The invention is not limited in its application to the details and construction and arrangement of parts illustrated in the accompanying drawings since the invention is capable of other embodiments that are being practiced or carried out in various ways. Also, the phraseology and terminology employed herein are for the purpose of description and not of limitation. 
     DETAILED DESCRIPTION OF THE INVENTION 
     Description of the Preferred Embodiment(s) 
     Referring to FIG. 1 a typical first in-situ groundwater treatment system is shown generally at  10 . The improvement of this invention is shown generally at  12 . Under normal condition groundwater  14  flows though an aquifer  16 . A zone of contamination  18 , within the aquifer  16 , contains manmade or natural impurities that have entered the aquifer  16  and which contaminants are carried by the flow of groundwater  14 . The typical first in-situ treatment system  10  includes a trench or repository  20  formed within the aquifer  16 , generally perpendicular to the flow of groundwater  14  through the aquifer  16  and down to the underlying bedrock  22 . The repository is filled with primary treatment media  24 , such as active metals, activated carbon, limestone, or a biological agent. Typically, when the repository  20  is to be placed across the aquifer  16  for a significant distance, a portion of the repository may be filled with an impermeable material to form a barrier  26  across the aquifer  16 , as shown in FIG.  2 . The lower cost barrier  26  helps to reduce the overall cost of the treatment system by reducing the amount of primary treatment media  24  needed to neutralize the zone of contamination  18  within the groundwater  14 . The barrier  26  redirects the flow of groundwater  14  to that section of the repository  20  containing the primary treatment media  24  and funnels the zone of contamination  18  through the primary treatment media  24 . 
     Groundwater  14  exiting the first treatment system  10  may contain the neutralized contaminants and secondary contaminants  28  dissolved into the groundwater  14  from the primary treatment media  24 . When active metals, such as iron (either elemental or zero valent iron), copper or other metals are used, the resulting secondary contamination  28  may require the need for additional processing before the groundwater  14  can be used as potable water. The treatment provided by the secondary treatment system  12  of this invention neutralize the secondary contaminants  28  introduced into the groundwater  14  by the primary treatment media  24 . The secondary contaminants  28  are in the form of soluble salts or compounds of the metal from which the primary treatment media is made. The secondary treatment system  12  of this invention consists of a second trench or repository  30  downstream of the first treatment system  10  so as to further treat the groundwater  14  containing the secondary contaminants  28 . The second repository  30 , like the first repository, is excavated down to bedrock  22  and parallels the primary treatment system. A porous or perforated tube  32  is placed adjacent to the bedrock  22 . A porous fabric material may be placed around the perforated tube  32  in order to prevent soil or clay from entering the perforated tube  32  and forming an obstruction. Porous media  34  is placed over the perforated tube  32  to fill the space between the bedrock  22  and a distance approximately 0.5 to 1 foot below the normal ground level  36 . Vent tubes  38  are inserted into the porous media  34  at selected distances from one another. The vent tubes  38  enter the porous media  34  to provide pressure relief for the secondary system. The space between the top  40  of the porous media  34  and ground level  36  may be filled with an appropriate material such as soil or fine gravel. 
     A flow of oxygenated gas  42  is passed though the porous media  34 . The source of oxygenated gas can be compressed oxygen stored in tanks (not shown), a compressed gas stored in a tank wherein the gas contains from 15 to 40 volume percent oxygen, or compressed air provided from a storage tank or a standard air compressor. The preferred source of the oxygenated gas is to provide ambient air with the aid of a compressor. The gas flow rate should be at level sufficient to convert a substantial portion of the secondary contaminant  28  of solublized metal-based primary treatment media into insoluble oxides prior to the exit of the groundwater  14  from the secondary treatment system. The groundwater  14  containing secondary contaminants  28  enters the secondary treatment system  12  where it is oxygenated by the flow of oxygenated gas  42  through the porous media  34 , thereby altering the secondary contaminants  28  to an insoluble oxide and removing the secondary contaminants  28  from the groundwater  14 . 
     An alternative primary treatment system for use with the improvement of this invention is shown in FIG.  3 . In this embodiment, a tank or semi-rigid container  46  containing the primary treatment media  24  encompasses the primary treatment system  48 . With this embodiment the groundwater  14  is channeled to the primary treatment system  48  by appropriate means, such as a collection system  50  in conjunction with an impermeable barrier  52  or by directly pumping the groundwater to the tank. The effluent  54  from the semi-rigid container  46  may contain the neutralized contaminants and secondary contaminants  56  dissolved into the groundwater  14  from the primary treatment media  24 . Prior to being returned to the groundwater  14  the effluent is treated by a secondary treatment system  58 , similar to that discussed hereinabove. This secondary treatment system  58  may in the form shown generally at  12  (in FIG. 1) or it may be a secondary tank system  60  containing a source of oxygenating gas  62  and porous media  64 . This arrangement may be in-situ (below ground level) or ex-situ (above ground level) 
     Thus, in accordance with the invention, there has been provided a method to remove iron and manganese impurities present in groundwater due to a primary in-situ groundwater treatment material. 
     With this description of the invention in detail, those skilled in the art will appreciate that modification may be made to the invention without departing from the spirit thereof. Therefore, it is not intended that the scopes of the invention be limited to the specific embodiments that have been illustrated and described. Rather, it is intended that the scopes to the invention be determined by the scope of the appended claims.