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BACKGROUND OF THE INVENTION 
       [0001]    The present invention generally relates to apparatus and methods for providing vapor barriers and, more specifically, to apparatus and methods of inhibiting the migration of harmful vapors from the ground. 
         [0002]    Many parcels of land are contaminated with harmful substances. Some sites may be contaminated by naturally occurring substances, such as Radon, or Methane. More commonly, sites are contaminated by industrial or commercial uses. For example, land and groundwater often becomes contaminated by factories, chemical processing plants, dry cleaning facilities, gasoline service stations, landfills and other facilities. When such parcels of land are no longer needed for these operations, they may sit idle because of the high cost of removing the contaminants. 
         [0003]    In some cases, land has been contaminated by such high levels of hazardous waste or pollution that it is considered un-developable. Such sites are sometimes designated as hazardous waste sites or Superfund sites. In other cases, the level of contamination, and the cost to restore the land, may be low enough that the land is a candidate for redevelopment. In the U.S., such sites are often referred to as “Brownfields”. There has been an increase in the number of developments on Brownfields partly because these sites often exist in high-population density areas where there is a great demand for developable land. 
         [0004]    Because of these trends, there has been an increased demand for economical ways to make Brownfields suitable for redevelopment. In some cases the contaminants may be removed. In many cases, however, it is either not possible, or practical, to remove all of the contaminants. In these cases, development may still be possible if ways are found to protect future occupants of the site from exposure to the hazardous substances at the site. One way to do this is to incorporate a barrier beneath newly constructed buildings that will inhibit the upward migration of chemical contaminants into the construction materials and indoor air space of the structure. 
         [0005]    Unfortunately, past techniques for providing effective barriers to hazardous substances to make land safe for redevelopment have had a number of drawbacks, including high cost and difficulties in installation, or they may have not provided an adequate level of isolation from contaminant vapors. For example, various forms of polyolefin sheeting have been used as barriers to contaminant vapor intrusion. These may comprise low and medium density polyethylene, which is laid down in an overlapping pattern. The overlaps are then chemically sealed or heat welded to produce a continuous sheet. Penetrations through the membrane (e.g. sewer piping, electrical conduit, etc.) are sealed by wrapping and mechanically binding the membrane to the penetrating object. The use of these membrane materials for vapor barrier application is very labor intensive as the seam binding/welding and mechanical sealing of penetrations requires significant time by skilled technicians to ensure membrane integrity. 
         [0006]    Latex modified asphalt sprays have also been used as a low cost alternative vapor barrier. Typically, the material is spayed onto the ground surface. In some cases, the asphalt may be applied over a typical geo-textile fabric, which serves to add tensile strength, but is not a barrier to vapor movement. During application, when encountering a penetration (e.g. conduit protruding upward) sealing around the protrusion is easily accomplished by spraying the asphalt-based material from the ground surface up to and contacting the protrusion, thus making a continuous seal. Asphalt-based membranes have been shown to perform well as barriers to water, but have limited ability to inhibit volatile organic vapors (e.g. gasoline, degreasing solvents, etc.) commonly found on previously polluted properties. In fact these membranes will be degraded by many of the chemicals commonly found on polluted sites (benzene, perchloroethene, etc.). 
         [0007]    As can be seen, there is a need for improved ways to provide a barrier to hazardous materials that protects occupants of contaminated land, in a way that is effective, economical and easy to install. There is also a need for a contaminant vapor barrier that is easy to install on buildings which have penetrations through the barrier surface. There is also a need for a contaminant vapor barrier that is not degraded by the chemicals present on polluted sites. 
       SUMMARY OF THE INVENTION 
       [0008]    In one aspect of the present invention, a composite membrane comprises: a first layer of high-density polyethylene (HDPE); a layer of asphalt applied over the first layer of HDPE; and a second layer of HDPE sheeting applied over the layer of asphalt. 
         [0009]    In another aspect of the present invention, a method of creating a composite barrier to chemical vapors comprises: applying a base layer comprising high density polyethylene (HDPE); applying an asphalt layer over the base layer; and applying a top layer comprising HDPE over the asphalt layer. 
         [0010]    In a further aspect of the invention, a method of constructing a building comprises: applying a base layer comprising polyethylene against a ground surface; applying an asphalt layer against the base layer; applying a top layer comprising polyethylene against the asphalt layer; and pouring a concrete layer against the top layer. 
         [0011]    These and other features, aspects and advantages of the present invention will become better understood with reference to the following drawings, description and claims. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0012]      FIG. 1  is a partial perspective cut-away view of a partially constructed building utilizing the composite contaminant vapor barrier according to an embodiment of the present invention; 
           [0013]      FIG. 2  is cross-sectional view of a below-grade floor of a building having overlapping sections of a composite contaminant vapor barrier according to an embodiment of the present invention; 
           [0014]      FIG. 3  is a cross-sectional view of a composite contaminant vapor barrier according to an embodiment of the present invention; and 
           [0015]      FIG. 4  is a flow chart of a method of preventing contaminant vapors from entering a building. 
       
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
       [0016]    The following detailed description is of the best currently contemplated modes of carrying out the invention. The description is not to be taken in a limiting sense, but is made merely for the purpose of illustrating the general principles of the invention, since the scope of the invention is best defined by the appended claims. 
         [0017]    The present invention generally provides a composite membrane system that may be placed directly on the ground surface prior to erecting a building on site. The resulting membrane system serves to inhibit vapors from upward migration into the construction materials and indoor air space of the structure. The composite membrane system of the present invention may be employed horizontally, beneath a concrete floor. Alternatively, embodiments may be employed in vertical configurations, such as between a below-grade wall and the adjacent soil. The present invention may also find applications on contaminated sites besides buildings, for example, to provide a contaminant vapor barrier under playgrounds and other recreational developments or under parking lots. The present invention may also provide protection from a range of contaminant vapors including those from petroleum-based products and chlorinated hydrocarbons. 
         [0018]    Embodiments of the invention may provide a composite membrane system comprising various combinations of polyethylene sheeting and latex modified asphalt. The composite membrane system may be placed between the foundation of a building and the soil pad to eliminate vapor exposure pathways and to stop contaminated vapors from permeating through the slab. The present invention is not susceptible to chemically induced materials breakdown, punctures, and seam weakness resulting from poor detail work and/or application installation imperfections around penetrations. In some prior vapor barrier systems, asphaltic layers were susceptible to chemical breakdown. Prior vapor barriers employing polyethylene sheeting were difficult to install and were prone to vapor pathways around penetrations or seams. 
         [0019]      FIG. 1  is a partial perspective cut-away view of a partially constructed building utilizing the composite membrane contaminant vapor barrier system according to an embodiment of the present invention. The vapor barrier  10  is installed directly on the soil  12  of a building pad. A concrete slab floor  14  is installed on top of the vapor barrier  10 . The floor  14  may be part of a building  16 , which includes a wall  18  and a footing  20 . 
         [0020]    The vapor barrier  10  is constructed on-site by laying down a base layer  22 , which may comprise HDPE sheeting, directly onto the building pad soil  12 . HDPE provides chemical resistance, high tensile strength, and stress-crack resistance. The edges of individual sections of the base layer  22  are overlapped and bonded together, as described below. 
         [0021]    A core layer  24  of asphalt in an emulsion form is layered directly over the base layer  22 . The core layer  24  may comprise an elastic co-polymer modified asphaltic membrane that may be spray-applied or applied by hand directly over the base layer  22 . The core layer  24  provides additional protection against vapor transmission and insures proper sealing of potential vapor pathways. The core layer also serves to secure the overlapping edges to the base layer  22  as well as attach the vapor barrier  10  to the building surfaces. The core layer  24  also creates an effective seal around slab penetrations, such as pipes, conduits and building structures that penetrate the vapor barrier  10 . One example of a penetration is pipe  28  which protrudes through an opening  30  in the vapor barrier  10 . As a result, the need for expensive mechanical fastening at termination points is eliminated. Furthermore, the core layer  24  serves to protect the base layer from potential damage during construction on the site. 
         [0022]    A bond layer  26  is applied over the core layer  24 . The bond layer  26  may comprise the same material as the base layer  22 , which in the present embodiment is HDPE. The bond layer  26  helps protect the system from getting punctured after installation and provides a final layer of chemical resistance. The resulting vapor barrier  10  with the combination of the base layer  22 , the core layer  24  and the bond layer  26  is a vapor barrier that is resistant to even very concentrated chemical pollutant vapors, is puncture resistant and is economical to install. 
         [0023]      FIG. 2  shows a cross-sectional view of a below-grade floor of a building having overlapping sections of the vapor barrier according to another embodiment of the present invention. In this embodiment, two overlapping adjacent sections of the vapor barrier are shown. In particular, a vapor barrier  32  is shown overlapping an adjacent vapor barrier  34 . Vapor barriers  32  and  34  may each include a base layer  36 , a core layer  38  and a bond layer  40  that are similar to the corresponding layers shown in  FIG. 1 . Vapor barriers  32  and  34  are installed directly on the soil  42  of the building pad. A floor  44  comprises a poured concrete slab installed directly over the vapor barriers  32  and  34 . 
         [0024]    In the region where vapor barriers  32  and  34  overlap, an additional asphaltic layer  50  may be applied between the two layers. This insures that the two layers are firmly and sealingly attached to each other. This asphaltic layer may be identical to the core layer  38  and may be applied in the same manner as the core layer  38 . In other embodiments, other sealing materials may be applied to form a seal between the two vapor barriers  32  and  34 . Also, in additional embodiments, instead of overlapping the vapor barriers  32  and  34 , the edges of the two vapor barriers may be placed adjacent to each other and a sealing material placed across the edges. In other embodiments, one or both of vapor barriers  32  and  34  may be entirely, or partially, disposed in a vertical orientation, for example, against a vertical wall of soil (not shown). In this vertical orientation, a below-grade concrete wall (not shown) may be installed on the side of the vapor barrier opposite the soil. 
         [0025]      FIG. 3  shows a cross-section of a composite vapor barrier  52  in accordance with an alternative embodiment of the invention. Vapor barrier  52  includes base  54 , core  56  and bond  58  layers, as described above. However, in this embodiment, the base  54  and bond  58  layers have an additional layer added to them. In particular, the base layer  54  includes an HDPE layer  60  with a geo-textile layer  62  bonded to its bottom surface. Geo-textile layer  62  provides a friction course between the base layer  54  and the soil. This inhibits movement between the base layer  54  and the soil during installation. The geo-textile layer  62  may comprise a coating of unwoven spun polypropylene fibers. In one embodiment, the base layer  54  comprises the product Geo-Seal Base, core layer  56  comprises the product Ecoline S, and the bond layer  58  comprises the product Geo-Seal Bond, all three products being available from Land Science Technologies Division of Regenesis Corporation of San Clemente, Calif. 
         [0026]    The core layer  56  may be identical to the core layers  24  and  38  described above. The bond layer  58  may comprise a layer of HDPE  64  with a geo-textile layer  66  bonded to its top surface. Like the geo-textile layer  62 , geo-textile layer  66  may comprise a coating of unwoven spun polypropylene fibers. The geo-textile layer  66  provides and effective bond between the vapor barrier  52  and the adjacent concrete slab. 
         [0027]    The bond layer  58  may also have a series of perforations  68  passing through it. These perforations may serve two functions. They allow for water vapors that occur upon the dehydration curing of the latex modified asphalt in the core layer  56  to move upwards. Also, upon laying the concrete structural slab on the bond layer, the perforations  68  allow water penetration and vaporization to aid in the curing of the concrete slab. 
         [0028]      FIG. 4  shows a flow chart of a method of preventing contaminant vapors from entering a building. In step  72  a sheet of the base layer is applied to the soil. This may comprise, for example base layers  22 ,  36  or  54 . This step may also include adding openings for penetrations, such as opening  30 . The core layer is then applied on the base layer in step  74 . This may comprise core layer such as core layers  24 ,  38  or  56 . In step  76  the base layer is also applied to the penetrations and edge regions of the base layer. This may include penetrations, such as pipe  28  and opening  30  as well as the perimeter edges of the base layer. 
         [0029]    In step  78 , the bond layer, such as bond layers  26 ,  40  or  58 , is applied to the core layer. In step  80  an additional core layer may be applied to the top of the bond layer where it will overlap with an adjacent vapor barrier. For example this may comprise the region of bond layer  50  as shown in  FIG. 2 . Finally, a concrete slab is installed on top of the bond layer in step  82 . This slab may be, for example, slab  14 ,  44  or  49 . 
         [0030]    As can be appreciated by those skilled in the art, the present invention provides a composite contaminant vapor barrier system and method. The vapor barrier may be economically installed on-site directly on contaminated soil. The vapor barrier is effective in inhibiting the upward migration of vapors into a building constructed over the vapor barrier. The vapor barrier is resistant to puncturing. Penetrations, such as pipes, passing through the vapor barrier are easily sealed by the sprayed-on core layer. Also, the materials used in the vapor barrier are not susceptible to chemical breakdown. 
         [0031]    It should be understood, of course, that the foregoing relates to exemplary embodiments of the invention and that modifications may be made without departing from the spirit and scope of the invention as set forth in the following claims.

Summary:
A composite membrane comprises: a first layer of high-density polyethylene (HDPE) and a layer of asphalt applied over the first layer of HDPE. A second layer of HDPE sheeting is applied over the layer of asphalt. A method of creating a composite barrier to chemical vapors is also disclosed which comprises applying a base layer comprising high density polyethylene (HDPE); applying an asphalt layer over the base layer; and applying a top layer comprising HDPE over the asphalt layer.