Abstract:
Disclosed is a system for filtering and distributing fluids to the subterranean soil environment. The system includes spaced core sheets that are typically partially enveloped with fluid permeable fabric. In one embodiment the core sheets are arranged in an alternating wide and narrow configuration. Fluid is transferred from a pipe to the core sheet edges and travels along the core sheets and through the fabric into the subsurface environment. In another embodiment a transfer sheet is provided adjacent at least some of the core sheet edges. Fluid is transferred from a pipe to the transfer sheet for subsequent distribution to the core sheet edges for travel along the core sheets and through the fabric into the subsurface environment.

Description:
This application claims the benefit of U.S. Provisional Patent Application No. 60/261,441, filed Jan. 12, 2001. 
    
    
     This invention relates generally to systems for filtering and distributing fluids to the subterranean soil environment. More particularly, this invention relates to a system capable of filtering and distributing fluid leachate from a septic tank or the like to the subterranean subsoil environment. 
     BACKGROUND OF THE INVENTION 
     Subterranean fluid leachate carrying systems are known in the prior art. In the system described in U.S. Pat. No. 4,880,333, a plurality of parallel core sheets of identical geometry are wrapped with a leachate permeable geotextile fabric so as to provide a continuous, horizontally extending in-drain for placement in an excavation. The system is preferably buried in a layer of sand or other fill. Leachate can be fed from a septic system or tank through a wide fluid conduit provided over the in-drain. The wide fluid conduit distributes the leachate over substantially the entirety of the top of the in-drain for subsequent distribution along the core sheets to the subsoil environment. It has been asserted that when identical parallel core sheets of the type used in U.S. Pat. No. 4,880,333 are stacked together with only a geotextile fabric as separation between them, during back filling and/or handling of the system the initially separated core sheets with the wrapped geotextile fabric may be compressed, one core sheet nesting into the other. This nesting leads to areas of the overall system, which are less efficient at filtration and distribution of leachate to the subsoil environment. Additionally, as the geotextile fabric permeability may lessen due to, for example, biological growth, the leachate level around the adjacent core sheet rises. However, the system of U.S. Pat. No. 4,880,333 does not provide a mechanism to redistribute the leachate accumulation from one core sheet to another core sheet, decreasing the long-term efficiency of the system. 
     The system described in U.S. Pat. No. 6,048,131 discloses a plurality of parallel, alternating core sheets and spacers of specified dimension, wrapped in an over and under serpentine fashion with a leachate permeable geotextile fabric so as to provide a continuous, horizontally extending in-drain for placement in an excavation. The spacers comprise inert material such as perlite sandwiched between spacer sheets of different pitch diameter than the core sheets. The system is preferably buried in a layer of sand or other fill so that leachate can be fed from a septic system or tank through a fluid conduit overlying the in-drain for purposes of distributing the leachate downwardly through the in-drain to the subsoil environment. The disclosure of U.S. Pat. No. 6,048,131 asserts that use of alternating sizes of core sheets and spacers lessens the tendency of the core sheets to nest. This reference also briefly mentions the use of perforated core sheets and states that the perforations bleed leachate through the fabric into the adjacent spacer. This system does not provide a mechanism for leachate movement to non-adjacent core sheets or spacers. Thus, an optimum mechanism to redistribute leachate accumulation from one core sheet to another core sheet is not provided. 
     SUMMARY OF THE INVENTION 
     An object of the invention is to provide an improved system for filtration and distribution of fluid into the subsoil environment. 
     Another object of the invention is to provide a leachate filtration and distribution system that can efficiently transfer leachate accumulating in one part of the system to other parts of the system. 
     A further object of the invention is to provide an improved leachate filtration and distribution system comprising core sheets and geotextile fabric with increased subsurface contact area. 
     Briefly stated, one aspect of the present invention is an assembly comprising a plurality of parallel, alternating core sheets and spacers and at least one transfer sheet adjacent an edge of at least some of the plurality of core sheets. The spacers can be in sheet form. 
     The core sheets and spacer sheets of the present invention are separated by a leachate permeable geotextile fabric. The geotextile fabric may be wrapped in an over and under serpentine fashion to leave the tops of the core sheets uncovered, but the tops of the spacer sheets covered. Alternatively, the fabric may be disposed between selected core sheets and spacer sheets in other patterns to leave any of the tops or bottoms of any of the core sheets and/or spacer sheets uncovered. 
     The transfer sheet of the present invention functions to transfer fluid from a supply pipe to the adjacent edges of a plurality of core sheets, for subsequent distribution along a core sheet and through the geotextile fabric into the subsoil environment. Additionally, any fluid accumulating in the area of a first core sheet can flow to the transfer sheet and thereby be redistributed to any other core sheet. The transfer sheet can be variously oriented to the edges of the core sheets. The core sheets, spacer sheets and transfer sheet are preferably secured together, for example with bands or straps. The secured assembly can be overwrapped with geotextile fabric to form a system or indrain. 
     Another aspect of the present invention is a system comprising a plurality of alternating wide and narrow core sets. Each core set is comprised of parallel, alternating core sheets and spacer sheets. Fabric is disposed between some or all of the core sheets and spacer sheets. The alternating wide and narrow core sets provide multiple outwardly extending arms. The outermost ends of the arms are overwrapped with geotextile fabric. The outwardly extending arms function to provide a geometrical surface area advantage by increasing the system sidewall/soil surface interface area for a given length of leachate system, thereby enhancing leachate drainage to the subsoil environment. 
     In yet another aspect of the invention the leachate system comprises a plurality of alternating wide and narrow core sets and a transfer sheet adjacent to at least some of the core sheets. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     FIG. 1 is a partial, schematic, side view of one aspect of the invention illustrating a spacer sheet disposed between two core sheets, the assembly wrapped with geotextile fabric; 
     FIG. 2 is a view similar to FIG. 1, illustrating a different embodiment of the invention; 
     FIG. 3 is an schematic, top plan view, partially in phantom, of one aspect of the invention illustrating alternating wide and narrow core sets; 
     FIG. 4 is a partial, schematic, top plan view of another aspect of the invention, illustrating parallel core sheets separated by spacer sheets (shown in phantom) and a transfer sheet perpendicular to the core sheets; 
     FIG. 5 is a schematic, top plan view of another aspect of the invention, illustrating wide and narrow core sets with a transfer sheet perpendicular to the core sheets; 
     FIG. 6 is a schematic end view of an embodiment of the invention having a fluid supply (shown in section) overlying a vertically arranged transfer sheet (also shown in section); 
     FIG. 7 is a view similar to FIG. 6, showing another embodiment of the invention; 
     FIG. 8 is a view similar to FIG. 1, illustrating another embodiment of the invention; 
     FIG. 9 is a schematic end view of an embodiment of the invention having horizontally arranged transfer sheets; 
     FIG. 10 is a view similar to FIG. 9, showing another embodiment of the invention having angularly arranged transfer sheets; 
     FIG. 11 is a view similar to FIG. 1, illustrating an aspect of the invention wherein geotextile fabric sheets are disposed between alternating core sheets and spacers to leave the top and bottoms of the core sheets and spacers uncovered; and 
     FIG. 12 is a view similar to FIG. 6, illustrating another aspect of the invention. 
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
     As shown in FIG. 1, the invention in.broadest form encompasses a plurality of alternating parallel core sheets  10  and spacer sheets  12  arranged generally in parallel. The core sheets  10  and spacer sheets  12  are preferably comprised of a polymeric material or materials such as, for example, polystyrene, polyethylene or polypropylene, formed in a generally planar or sheet fashion and having a plurality of arrayed dimples or protrusions extending from one or both faces. The dimple sizes of the core sheets and spacer sheets can be chosen to minimize undesirable nesting of these sheets during handling and use. U.S. Pat. Nos. 4,490,072, 4,880,333 and 6,048,131, the entire disclosures of which are incorporated by reference herein, describe similar sheet materials. Thicknesses of the core sheets  10  and spacer sheets  12 , defined as the maximum distance from one face to the opposing face, is not believed to be critical to practice of the invention. 
     Other variations will occur to those skilled in the art. For example, the core sheet, as well as the spacer sheets, as used in the above-described embodiment of the invention, may be imperforate and formed from a continuous sheet to have a desired dimple shape. One or both of the core sheets and spacer sheets can be provided of a perforated material. Still another alternative would be to provide imperforate core sheets and/or spacer sheets with openings for purposes of transferring fluid from one side of such sheet to the other. A further alternative would be to provide porous core sheets and/or spacer sheets. A still further alternative is to provide partial spacer sheets, or a single or multiple non-sheet spacers between adjacent core sheets. 
     Fluid permeable geotextile fabric  14  is disposed between some or all of the core sheets  10  and spacer sheets  12 . The geotextile fabric is typically a polymeric, nonwoven needle-punched fabric known in the art. TNS R050 fabric available from TNS Advanced Technologies of Spartanburg, S.C. has been found suitable for this use. The fabric functions in one aspect to provide surface area for the formation of a biological mat. Fluid, such as leachate from a septic system is beneficially cleansed by the biological mat as it permeates through the fabric and mat into the soil. The fabric is advantageously disposed between sheets  10 ,  12  in an over and under serpentine fashion as shown in FIG.  1 . Naturally, other wrapping patterns (for example a side to side serpentine pattern) and spacings (for example under a core sheet/spacer/core sheet set, over a spacer, and under a core sheet/spacer/core sheet set as shown in FIG. 2) could also be used depending on the fabric surface area and flow paths desired. Alternatively, as shown in FIG. 11, geotextile fabric may be taken from a roll or in cut sheet form and placed adjacent a first side of a core sheet and a spacer sheet. Assembling alternating sequences of a core sheet, fabric sheet and spacer sheet provides a fabric/core sheet/fabric/spacer sheet set as shown in FIG.  11 . In this embodiment, the upper and lower edges of the core sheets and spacers may be left uncovered to aid in distribution of high leachate flows. Naturally, in any embodiment the patterns would be repeated as needed to arrive at a structure having a desired size and surface area. The geotextile fabric may be joined to the core sheet and/or spacer sheet by, for example, heat bonding, adhesive bonding or mechanical fastening, to make assembly easier. It should be understood that other, alternative fabric wrapping patterns and sheet and fabric spacings are within the skill of the ordinary practitioner and are fully comprehended by the present invention. Typically, in any embodiment, it is preferred that geotextile fabric is also disposed over the uncovered top, side and ends of a system (but typically not the bottom) to prevent soil infiltration into the system during backfilling. The previously mentioned TNS R050 fabric can be disposed over the top, sides and ends of the system. However, this fabric is prone to stretching and under some conditions the bands can stretch the fabric into the sides of the system. It has been found preferable in some applications to use a thinner and stiffer geotextile fabric to ease handling and minimize fabric stretch. TYPAR® 3401, available from Remay Industrial Fabrics, Inc. of Madison, Tenn., is a geotextile fabric that is stiffer than the TNS R050 fabric. TYPAR® 3401 has been found suitable for use adjacent the top, sides and ends of the system. TYPAR® 3401 also preferably minimizes infiltration of soil into the system. 
     In an embodiment of the invention shown in FIG. 8, the core sheets  10  and spacer sheets  12  have differing heights above the underlying soil bed  16 . When geotextile fabric  14  is disposed between the core sheets  10  and spacer sheets  12 , a portion of the core sheet  10  and fabric  14  is suspended above the underlying soil bed  16 . Suspension of the fabric  14  away from the underlying soil bed enhances biological growth on the fabric and thereby filtering efficiency of the system. 
     As shown in FIG. 3, another aspect of the present invention is a subsoil fluid distribution system  20  comprised of alternating wide  22  and narrow  24  core sets. Advantageously, an outermost edge of a wide core set  22  can extend about twelve inches beyond the edge of a narrow core set  24 . Preferably, the outermost edge of a wide core set  22  will extend from about three inches to about twelve inches beyond the edge of a narrow core set  24 . Each core set  22 ,  24  is comprised of alternating parallel core sheets  10  and spacers or spacer sheets  12  arranged in face to face order. Leachate permeable geotextile fabric  14  (not shown in FIG. 3 for clarity) is disposed between some or all of the core sheets  10  and spacer sheets  12 . Preferably, the fabric  14  is wrapped in a serpentine pattern over each spacer sheet  12  and under each core sheet  10  as shown in FIG.  1 . 
     With reference again to FIG. 3, the arm portions  26  of each wide core set  22  extending beyond the narrow core set  24  are covered with geotextile fabric, preferably in the form of a sock or sheath (not shown) placed over and secured to the arm  26 . A fabric stiffer than the TNS R050 fabric is advantageous for use in this application. 
     The wide  22  and narrow  24  core sets are placed in alternating sequence, and secured to each other, for example with straps or bands  28 , to form the inventive system  20 . 
     In use, the above system  20  is placed in a previously prepared excavation and supported on a soil bed  16 . A fluid supply  34  is placed adjacent the system  20 . It should be noted that the fluid supply  34  may be placed in orientations to the system  20  other than the one shown, (for example, within the system or adjacent the system side) and any and all orientations are included in the invention. The fluid supply  34  typically comprises perforated plastic pipe. An additional layer of geotextile fabric (not shown) can preferably be placed over the fluid supply  34  and top of the system  20  and over exposed edges of the sheets  10 ,  12  to prevent infiltration of the leachate system by the subsequently placed backfill. It should be understood that geotextile fabric  14  may be positioned and secured adjacent exposed edges of the system  20  during manufacturing. Backfill such as sand is placed around and over the system  20  and leachate supply  34 . In use, fluid such as leachate is carried by the fluid supply pipe  34 , and discharged over or into the system  20 . The leachate travels through the geotextile fabric underlying the pipe  34  (not shown in FIG. 3) and along the core sheets  10 , spacer sheets  12  and fabric  14  into the subsoil environment. The outwardly extending arms  26  of the wide core sets  22  function to provide a geometrical surface area advantage and increase the sidewall/soil interface area for a given length of leachate system  20 , thereby enhancing leachate filtration and drainage into the subsoil environment. Naturally, other configurations of core sheets  10  and spacer sheets  12  that provide increased sidewall/soil interface area would occur to those skilled in the art, for example polygonal or other arrangements, and all such variations are encompassed by this invention. 
     In another aspect of the invention partially shown in FIG. 4, a core set  40  comprising alternating parallel sequences of core sheets  10  and spacers or spacer sheets  12  is provided. Geotextile fabric  14  is disposed between some of the alternating sequences, preferably in the above described over and under serpentine fashion shown in FIG.  1 . In some variations certain of the core sheets  10  and under wrapped fabric  14  are raised as shown in FIG. 8, so that these core sheets and underlying fabric will be above the underlying soil bed  16  when the system  20  is in use. A transfer sheet  42  is placed adjacent to, or abutting, at least some of the edges  44  of the core sheets  10 . The transfer sheet  42  can be comprised of the same materials and in the same configurations as the core sheets  10 . The transfer sheet can be perforated or permeable to leachate. The transfer sheet does not have to extend over the entire depth of the core set edge to the underlying soil  16 , as shown in FIG. 6, but may extend along only a portion of the depth thereof. Naturally, multiple overlapping transfer sheets may be used to obtain coverage of substantially the entirety of all of the core sheet edges  44 . 
     Geotextile fabric  14  (not shown in FIG. 6 for clarity) can advantageously be disposed adjacent some or all of the transfer sheet  42  faces, transfer sheet top edge and transfer sheet bottom edge. The previously mentioned TNS R050 fabric can be used adjacent the transfer sheet  42 . However, this fabric is prone to stretching and under some conditions the core sheet edges  44  can stretch the fabric into contact with the transfer sheet  42 . It has been found advantageous in some applications to use a stiffer geotextile fabric to minimize fabric stretch. TYPAR® 3401 has been found suitable for use adjacent the transfer sheet  42 . 
     The core sets  40 , transfer sheet  42  and geotextile fabric  14  are secured together for handling, for example with plastic bands or straps to provide an assembly. Geotextile fabric  14  may be positioned and secured over the exposed top, side and/or edges of the assembly to prevent soil infiltration during later back filling. While a core set  40  on one side of the transfer sheet  42  has been described for clarity, it should be understood that core sets  40  on both sides of the transfer sheet  42  as shown in FIG. 6 are fully comprehended by the invention. In one preferred embodiment, a series of alternating core sheets  10  and spacer sheets  12  is wrapped serpentine fashion with fabric  14  as shown in FIG. 1 to form a core set. The core set may be secured with one or more straps or bands if desired. A transfer sheet  42  is disposed adjacent to, and perpendicular with, the exposed edges of at least some of the core sheets  10  to form an assembly. Additional fabric can be used to cover some or all of the ends and sides of the assembly, and the covered assembly is secured with straps or bands  28  to form a system  20 . Typically, the top of the system  20  is covered with geotextile fabric during installation of the system. 
     The transfer sheet  42  provides a route for fluid communication between the fluid supply  34  and some or all of the core sheets  10  as well as between some or all of the core sheets  10  and/or spacer sheets  12  themselves. The transfer sheet  42  (or multiple transfer sheets) may also be provided horizontally as shown in FIG. 9 or angularly as shown in FIG. 10 with respect to the core sets  40 . While two sheets  42  are shown in FIGS. 9 and 10 it is believed that additional sheets would be advantageous to maintain separation of the spaced core sets  40  when the assembly is secured. Provision of the transfer sheet or sheets other than vertically may require the transfer sheets to be permeable or perforate so that some leachate can pass therethrough. It is also preferred that transfer sheets in other than vertical orientations be arranged to prevent nesting and the resultant diminished leachate flow. The arrangements may include, for example, using transfer sheets with alternating dimple sizes or provision of spacers between adjacent transfer sheets. In other variations the transfer sheet edge abutting the core set is notched or slotted. The slotting allows the transfer sheet to interengage with the abutting core sheets as shown in FIG.  10 . 
     In one typical use, the above system  20  is placed in a previously prepared excavation  46  and supported on a soil bed  16  as shown in FIG. 6. A fluid supply pipe  34  is placed adjacent the system  20 . It should be noted that the fluid supply pipe  34  may be placed in orientations to the system  20  other than the one shown, (for example, within the system or adjacent the system side) and any and all orientations are included in the invention. At least a portion of the fluid supply pipe  34  typically comprises perforated plastic pipe. The fluid supply pipe  34  is fluidly connected to a fluid source such as a septic tank or septic system. A layer of geotextile fabric (not shown) can preferably be placed over the supply pipe  34  and top of the system  20  and over exposed edges of the sheets  10 ,  12  to prevent infiltration of the leachate system by the subsequently placed backfill. It should be understood that the layer of fabric  14  and/or supply pipe  34  may be positioned and secured adjacent the system  20  during manufacturing. Backfill such as sand is placed around and over the system  20  and supply pipe  34 . Leachate flows from the source through the pipe  34  into the system  20 , where it travels along the transfer sheet faces to an adjacent core sheet edge  44 . Leachate travels from the edge  44  along the core sheet faces and through the fabric  14  into the subsoil environment. The transfer sheet  42  typically provides leachate with a fluid communication route to all of the core sheets, improving leachate transfer, filtration and distribution into the soil environment. Additionally, any leachate accumulating adjacent one core sheet will flow by gravity back to the transfer sheet  42  and thence to any core sheet  10  with a lower leachate level. Thus, the present invention is less susceptible than previous systems to decreasing of leachate flow into the subsoil environment. Since the transfer sheet  42  provides a fluid communication path to all of the core sheets  10  and/or spacer sheets  12  of the system, particular dimensional relationships between the core sheets, spacer sheets and leachate supply are not needed. 
     In another embodiment shown in FIG. 5, the alternating wide  22  and narrow  24  core sets previously described may be provided on one or both sides of a transfer sheet  42  to form the subsoil fluid distribution system  20 . At present, the best method known for manufacture of this embodiment comprises manufacture of an alternating wide and narrow core set assembly as shown in FIG.  3 . The core set assembly is sectioned transversely into longitudinal sections  52 ,  54 . A transfer sheet  42  is disposed in the separation between each section  52 ,  54 . Fabric is disposed over the top, sides and ends of the sections end transfer sheet. The sections, transfer sheets and any geotextile fabric are secured, for example, with bands or straps. The use of alternating wide  22  and narrow  24  core sets in combination with a transverse transfer sheet  42  combines the benefits of additional system sidewall/subsoil interface area and leachate fluid communication between all of the core sheets  10  and spacer sheets  12 . 
     In another embodiment of the invention shown in FIG. 12, an angular transfer sheet  42  is disposed over portions of the top and portions of one edge  44  of a core set  40 . Advantageously, the transfer sheet is perforated and wrapped with geotextile fabric  14 . In one embodiment the fabric envelops the angular transfer sheet and the edges of the fabric  14  are over lapped and attached, as by, for example, sewing, thermal bonding or adhesive bonding. The fluid supply pipe  34  is positioned adjacent the angular transfer sheet. The fluid supply  34  may be covered with a separate layer of geotextile fabric. Alternatively, the geotextile fabric enveloping the angular core sheet can be sized to permit the insertion of the fluid supply as shown in FIG.  12 . In another variation, the angular transfer sheet  42  is disposed intermediate two core sets. In still another variation of the invention, multiple angular transfer sheets are disposed between multiple core sets. The angular transfer sheet functions to provide a fluid communication route from the supply to the edges of the adjacent core set or core sets. The angular transfer sheet also provides a fluid communication route between any core sheet or spacer sheet adjacent the transfer sheet. 
     Typically, the system will have a width of about four feet and a length of about four feet. Multiple systems can be placed end to end to provide any desired system length. It should be understood that the above dimensions are primarily due to commercial considerations and are not limitations on the present invention, which contemplates a broad range of system widths and lengths. In any embodiment where soil conditions do not allow desired system length, additional subsoil fluid distribution systems can be provided or multiple systems can be stacked vertically one above another. Another variation that will occur to those skilled in the art is to provide more than one fluid supply pipe, over a fluid distribution system of the type described above. 
     While preferred embodiments of the foregoing invention have been set forth for purposes of illustration, the foregoing description should not be deemed a limitation of the invention herein. Accordingly, various modifications, adaptations and alternatives may occur to one skilled in the art without departing from the spirit and scope of the present invention.