Abstract:
A method for installing and using paper-enclosed filter media units in an effluent treatment system. The paper-enclosed filter media units are preferably pre-filled off-site and transported to the installation site via commercial vehicle. The filter media units are then installed underneath the ground and connected to a treatment system. The filter media units contain at least one perforation and are preferably filled with expanded polystyrene (EPS) beads. In practice, the effluent enters the filter media unit through the at least one perforation in the filter media unit and trickles through the media where it is treated before being distributed beneath the filter media unit. The filter media unit preferably is comprised of a plurality of perforations, facilitating the entry of effluent in the filter media unit and the distribution of effluent into the ground. The method optionally is further comprised of a distribution grid which distributes the effluent horizontally across the top of the filter media unit.

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
       [0001]    This application is a continuation-in-part of U.S. application Ser. No. 12/184,850, now abandoned, which is a continuation in part of U.S. application Ser. No. 10/702,857 filed Nov. 6, 2003, abandoned, which is a continuation in part of U.S. application Ser. No. 10/994,809 filed Nov. 22, 2004, abandoned, which is a continuation in part of U.S. application Ser. No. 11/433,794, filed May 11, 2006, abandoned, which is a continuation in part of U.S. application Ser. No. 11/543,305 filed Oct. 4, 2006; which claims priority to U.S. Provisional Application Ser. No. 60/714,473 filed Sep. 6, 2005, and U.S. Provisional Application Ser. No. 60/723,507 filed Oct. 4, 2005, the disclosures of which are hereby incorporated herein in their entirety by reference. 
     
    
     BACKGROUND 
       [0002]    In the United States, a growing number of households rely upon a septic system rather than centralized wastewater treatment facilities. In fact, approximately one fourth of the households in the United States use a septic system to treat, filter, clean and disburse wastewater. A typical septic system consists of a septic tank, a distribution/filtration box, and some form of an underground disposal field. Several types of underground disposal fields have been developed and are known in the art. The most common type is a drainfield, also known as a leach field or absorption field. There have been several variations of drainfields, including mound systems, sand filters, and dig outs. 
         [0003]    Once sewage undergoes treatment in a septic tank, the resulting effluent is transported to the drainfield. This is accomplished by either gravity or through a mechanical pump, with the goal of uniformly discharging effluent below ground into the soil for final treatment and disposal. Another goal of the drainfield is to naturally filter the post-septic tank effluent to remove any remaining pathogens, bacteria or biomass prior to flowing into the ground water. Sizing of a drainfield depends upon several factors including the available area on the property, the number of individuals in the household, water usage habits of the household, on-site soil conditions, and government regulations. One typical form of a drainfield comprises a collection of multiple parallel-perforated pipes connected by one or more distribution pipes that allow distribution of effluent into the surrounding ground soil for filtration. 
         [0004]    Historically, construction of a drainfield has been expensive, time consuming, and inconvenient. Construction usually begins with the excavation of multiple trenches to lay the necessary perforated pipes. These trenches are usually less than 100 feet long and dug to create an essentially flat bottom. In one prior art drainfield construction, each trench is first filled with a layer of gravel. Next, a perforated pipe is placed in the trench, with an additional six-inch layer of gravel added to surround the perforated pipe. If required, a geotextile fabric or a similar product is placed over the gravel. Finally, a covering layer of backfill soil is added. This entire process requires transport of large amounts of gravel, backfill soil, and pipe from a distribution center to the drainfield site. The steps of digging trenches, creating a network of pipes, and laying different layers of filtering media requires specialized equipment, multiple experienced workers, time, and large quantities of natural resources (i.e., soil and gravel). 
         [0005]    In many areas of the country, unique soil conditions require a modified drainfield known as a mound or raised drainfield. In areas with a high groundwater level, shallow soil over impermeable soil, or slowly permeable soil, a mound must be created above ground to allow proper distribution and filtration of post-septic effluent. Above-ground mounds, however, often require a mechanical pump to raise effluent from the septic tank above ground to the mound. Second, a mound requires transport of additional natural resources to the site. Third, a mound is typically unsightly and greatly reduces the use and value of the land. Last, a mound requires a relatively larger area than a conventional drainfield and also requires routine monitoring and maintenance. 
         [0006]    One prior art alternative for a mound or raised drainfield is a sand filter that uses a water impermeable basin placed in the ground to contain a sand bed, with a network of perforated pipes located in the sand bed. The water impermeable basin is first filled with a layer of aggregate, most commonly pea gravel. Next, a second layer of medium grade clean sand is added to the basin to create the sand bed. A network of perforated pipes is placed on top of the sand bed, and a second layer of aggregate is then added to the basin. A larger perforated outflow pipe is typically placed within the basin for collection of filtered effluent that then enters the drainfield. 
         [0007]    Although sand filters may avoid the need for a mound, thus improving the appearance of the underground disposal field and allowing for better use of the ground, sand filters have several disadvantages. First, large volumes of heavy sand must be transported to the drainfield site, which can be very costly. Second, sand filters require very large cross sections to be effective. For example, a typical two-bedroom home typically requires a sand filter nineteen feet by nineteen feet in cross-section. Thus, these systems can only work with large acreage households. Third, most sand filters require a mechanical pump, resulting in greater energy and maintenance costs. 
         [0008]    A third type of drainfield called a “dig out” has also been used in the art. With a dig out, a large cross-sectional area of the soil near the septic tank is excavated to remove poor soil. Good quality soil is then transported to the site and evenly deposited in the excavated area. A network of perforated pipes is assembled and placed atop the newly deposited soil, which is connected to either a distribution box or directly to the septic tank. Backfill soil is then added over the network of perforated piping. While this method of creating a drainfield has some benefits with respect to a sand filter, the overall costs, manpower, and natural resources required to create a dig out system are significantly greater. 
         [0009]    There exists a need for alternative systems and methods to sand filters, mound drainfields, and dig outs for efficient treatment, filtration, and distribution of effluent. In addition, there is a need for filter media in such alternative systems and methods that is lightweight, portable, inexpensive, and that will allow for increased filtration so as to decrease the cross-sectional size of these systems. The benefits of such filter media would be welcome in more typical drainfield installations as well, where the need for a less labor-intensive, more cost-effective system is also needed. Finally, there is a need for such systems to be modular for easy transport to the drainfield site, allowing improved fabrication of these systems to further reduce overall costs. 
       SUMMARY 
       [0010]    The present invention is directed to apparatus, systems, and methods for treating effluent in difficult soil conditions that historically required an undesirable installation such as an elevated mound, a sand filter, or a dig out. The present invention is also directed to apparatus, systems, and methods for treating effluent in areas where more typical drainfield methods are used. In addition, the present invention is directed to apparatus, systems, and methods for use in other applications, such as the treatment of effluent using low volume treatment techniques. 
         [0011]    One embodiment of the present invention comprises a system for treating household effluent that includes a Mound Elimination Unit (“MEU”), a distribution grid, and filter media. (Note that the MEU is referred to as an “MRU,” for “Mound Reduction Unit,” in application Ser. No. 11/543,305.) The MEU is located downstream from a septic tank or similar discharge receptacle and is connected to the septic tank either directly or through an intermediate filtration subsystem. Aided by gravity, effluent leaves the septic tank and preferably travels to a filtration subsystem where it is treated with chlorine or any suitable agent to treat the effluent to remove bacteria and pathogens. The effluent then leaves the filtration unit through a second pipeline into the MEU. Within the MEU, a distribution grid uniformly distributes the effluent throughout the MEU, resulting in additional treatment and filtration of the effluent through a medium such as that described in U.S. Pat. No. 5,015,123 (“U.S. Pat. No. &#39;123”) or another suitable medium. In this way, levels of any remaining pathogens, bacteria, or human waste are significantly reduced. The treated and filtered effluent then leaves the MEU through an effluent transport, such as either a slotted linear grate or a series of screened portals, into a drainage unit where it is passed to a drainfield reserve. In appropriate circumstances, a pump is used to elevate the MEU outflow to the drainfield reserve. 
         [0012]    Filter media fills a large majority of the volume of the MEU. The filter media is comprised of a suitable material for filtering effluent, such as sand, pea gravel, soil, rock, expanded polystyrene (“EPS”), or some combination thereof. Preferably, the media is comprised of EPS beads with diameters of ⅛th inches or less. 
         [0013]    As mentioned earlier, the MEU houses a distribution grid. The distribution grid is positioned generally horizontally atop the filter media and in a preferred embodiment is constructed with a flat bottom so as to remain relatively stable atop the surface of the filter media. In the preferred embodiment, the distribution grid comprises a primary distribution member, lateral distribution arms, and a pipe adaptor. The pipe adaptor connects the primary distribution member to an inlet conduit. The inlet conduit conducts effluent into the distribution member through the pipe adaptor. The lateral distribution arms connect to the sides of the primary distribution member and extend laterally outward from it to span the surface of the filter media. Generally, three or more distribution arms extend from one side of the distribution member while two or more arms extend from the opposing side. Other configurations are possible, however. In the present embodiment, both the bottom of the primary distribution member and the bottoms of the lateral distribution arms contain perforations. As effluent flows throughout the distribution member and into the connected lateral distribution arms, it drains out through the perforations onto the filter media below. 
         [0014]    The distribution grid can be made of any resilient material. A durable, lightweight plastic is preferable. The shape and dimensions of the distribution grid can also be altered to conform to the requirements of the filter media with which it is used. In some installations, for example, a primary distribution member may need to be wider and longer. In others, the distribution member may need to be narrower or perhaps shorter. Similarly, the shape and dimensions of the lateral distribution arms and the pipe adaptor may need to be altered as well to conform to the size of the primary distribution member, the characteristics of the filter media, or both, so as to ensure that the distribution grid works together as one functional unit. 
         [0015]    It will, of course, be appreciated by those skilled in the art from the following detailed description that this innovative distribution grid can be used in conventional septic tank drainfield applications to achieve very favorable infiltrative capacity relative to prior art techniques, while at the same time permitting the use of shallower installations. 
         [0016]    Both the distribution grid and the MEU are sized to allow for easy transport to a drainfield site via a commercial vehicle. Distribution grids within multiple MEUs can also be connected to one another in parallel or in series to allow for one system to include multiple MEUs. 
         [0017]    Another embodiment of the present invention comprises a system for treating effluent that includes a MEU, a distribution grid, and preassembled filter media. In this embodiment, the preferred filter media is a collection of preassembled EPS-netted cylinders like those disclosed in U.S. Pat. No. &#39;123. The preassembled EPS-netted cylinders are comprised of EPS media packed into open netting. The EPS-netted cylinders may be arranged in multiple courses, each course stacked upon another. A distribution grid resides atop the uppermost course of cylinders. The bottom of the distribution grid is contoured in a convex shape so as to reside atop an EPS-netted cylinder with relative stability. Stability studs can also be used to further secure the distribution grid to a cylinder. The distribution grid is configured in generally the same fashion, and functions with the MEU in generally the same manner, as in the previous embodiment described earlier. 
         [0018]    In addition to the preassembled EPS-netted units, other types of preassembled filter media can be used in the MEU as well. Among these are EPS-filled paper units, including EPS-filled paper cylinders, rectangular EPS-filled paper bags, and rectangular EPS-netted bags. These types of preassembled filter media can also be used in more typical drainfield applications, as discussed later. EPS-filled paper units are also the subject of further embodiments of the present invention, as also discussed later. 
         [0019]    Another embodiment of the present invention is a method and apparatus for manufacturing preassembled EPS-netted units. The method and apparatus takes advantage of the efficacies of using a blower to produce the units, such as the elimination of undue static buildup on the pieces of EPS media. To produce an EPS-netted unit, netted material is placed over the exhaust outlet of a blower. The blower then blows EPS media into the netted material until the netting is filled to a desired capacity. The open end of the filled netted unit is then tied off, thereby creating a preassembled EPS-netted unit. The method and apparatus allow for the manufacture of EPS-netted units in a variety of lengths as well as in a range of diameters. The present embodiment envisions manufacturing EPS-netted units with a diameter from eight inches up to twenty inches. Other diameters, however, are also possible. 
         [0020]    Another embodiment is a method and apparatus for manufacturing preassembled EPS-filled paper cylinders. An EPS-filled paper cylinder comprises perforated paper tubing into which EPS media is blown to fill the paper tubing to create an EPS-filled paper cylinder. The paper cylinders can be created in various lengths as well as in a range of diameters. The present embodiment envisions manufacturing paper cylinders with a diameter from eight inches up to twenty inches. Other diameters, however, are also possible. 
         [0021]    The paper tubing of a preassembled EPS-filled paper cylinder serves as built-in barrier material. In more typical drainfield applications, the paper tubing functions like a geotextile fabric or similar product that is placed over aggregate or other filter media prior to covering the aggregate or filter media with backfill soil. This built-in functionality of the paper cylinders eliminates the need for such geotextile fabric or similar products in more typical drainfield installations. 
         [0022]    Another embodiment comprises a more typical drainfield for treating wastewater, such as household effluent. The drainfield includes a distribution grid and preassembled EPS-filled paper cylinders, like the kind described in the previous preferred embodiment. Generally, multiple preassembled EPS-filled paper cylinders are aligned side by side in an excavated trench. A distribution grid is set horizontally atop the EPS-filled paper cylinders, with the primary distribution member positioned atop the middle of the cylinders. The bottom of the primary distribution member is contoured in a convex shape so as to reside atop one of the EPS-filled paper cylinders with relative stability. Stability studs can also be used to further secure the primary distribution member to the paper cylinder. The entire drainfield is then covered with backfill soil. The paper tubing eliminates the need for using geotextile fabric or similar products prior to filling the excavated trench with soil. From its position atop the paper cylinders, the distribution grid is able to distribute effluent over a greatest volume of filter media, that filter media that is encased within the paper cylinders aligned side by side or beneath it. 
         [0023]    Note that an alternate embodiment contemplates a drainfield comprising a distribution grid and preassembled EPS-netted cylinders. In this instance, the drainfield is covered with a geotextile fabric or similar product prior to filling the excavated trench with soil. 
         [0024]    Another embodiment includes a method and apparatus for creating rectangular, preassembled, EPS-filled paper bags. An EPS-filled paper bag comprises perforated paper bag material into which EPS media is blown to fill the paper bag. In this embodiment, paper bag material is restrained within a jig prior to filling. The jig maintains the dimensions of the paper bag material as it is filled with ESP media, thus maintaining a generally standard rectangular shape from paper bag to paper bag. The dimensions of the jig are adjustable, allowing for the manufacture of paper bags of various shapes, widths, lengths, and heights. 
         [0025]    Another embodiment of the present invention comprises a more typical drainfield for treating wastewater, such as household effluent. The drainfield includes a distribution grid and one or more of the above-described rectangular, preassembled, EPS-filled paper bags. If an EPS-filled paper bag is of sufficient width, then only one paper bag is required for the drainfield. If one paper bag is not of sufficient width, then generally three or more preassembled EPS-filled paper bags are aligned side by side in an excavated trench. A distribution grid is set horizontally atop the EPS-filled paper bags, with the primary distribution member positioned atop the middle of the bags. If only one paper bag is used, then the primary distribution member is positioned along the center of the bag. In this embodiment, the bottom of the primary distribution member is flat so as to reside atop the EPS-filled paper bag with relative stability. Stability studs can also be used to further secure the primary distribution member to the paper bag. The entire drainfield is then covered with backfill soil. The paper skin of the EPS-filled paper bags eliminates the need for using geotextile fabric or similar products prior to filling the excavated trench with soil. From its position atop the paper bags, the distribution grid is able to distribute effluent over a greatest volume of filter media. 
         [0026]    A further embodiment of the present invention is comprised of a method for installing and using EPS-filled paper-enclosed filter media units. This method eliminates the necessity of having to fill the filter media units at the installation site, which requires a filling machine to be transported to the site and time to be spent on-site. Instead, the filter media units are filled with media off-site and then transported to the site, where they are installed beneath the ground and connected to an effluent treatment system. The filter media units preferably are tubular in shape such that they are easily stacked and loaded for transport. As described above, the filter media units contain at least one perforation for the entry of effluent, and preferably are filled with EPS beads that are ⅛th inch or less in diameter. In practice, the effluent enters the filter media unit through the at least one perforation and trickles through the media where it is treated before being distributed into the ground beneath the filter media unit. Preferably, the filter media unit is comprised of a plurality of perforations, thereby facilitating the entry of effluent in the filter media unit and the distribution of effluent into the ground. The method optionally is further comprised of a distribution grid which distributes the effluent horizontally and evenly across the top of the filter media unit. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0027]    Embodiments of the apparatus, systems, and methods of this invention are described by way of example with reference to the accompanying drawings in which: 
           [0028]      FIG. 1  is a cross-sectional schematic view of a system utilizing an MEU; 
           [0029]      FIG. 2  is a top schematic view of an embodiment of the present invention in which a distribution grid is used in conjunction with an MEU; 
           [0030]      FIG. 3  is a cross-sectional perspective view of another embodiment in which a distribution grid is used in conjunction with an MEU employing preassembled filter media; 
           [0031]      FIG. 4  is a perspective view of the distribution grid and a portion of the preassembled filter media shown in  FIG. 3 ; 
           [0032]      FIG. 5  is an exploded perspective view of the distribution grid shown in  FIG. 4 ; 
           [0033]      FIG. 6  is a perspective view of the bottom of a lateral distribution arm, which is a component of a distribution grid; 
           [0034]      FIGS. 7-9  are top schematic views of alternate configurations for employing multiple distribution grids to connect together multiple mound elimination units in a system; 
           [0035]      FIG. 10  is a schematic view of another embodiment in which a drainfield comprises a distribution grid and preassembled EPS-filled paper cylinders; 
           [0036]      FIG. 11  is a perspective view of the drainfield shown in  FIG. 10 ; 
           [0037]      FIG. 12  is a perspective view of another embodiment in which a drainfield comprises a flat-bottomed distribution grid and a rectangular, preassembled, EPS-filled paper bag; 
           [0038]      FIG. 13  is a perspective view of a second version of the drainfield shown in  FIG. 12  in which multiple rectangular, preassembled, EPS-filled paper bags are employed; 
           [0039]      FIG. 14  is a schematic view of another embodiment in which a method and apparatus are used to manufacture preassembled EPS-netted cylinders; 
           [0040]      FIG. 15  is a schematic view of another embodiment in which a method and apparatus are used to manufacture preassembled EPS-filled paper cylinders; 
           [0041]      FIG. 16  is a top schematic view of another embodiment in which a method and apparatus are used to manufacture rectangular, preassembled, EPS-filled paper bags; 
           [0042]      FIG. 17  is a perspective view of a primary distribution member, which is a component of the distribution grid shown in  FIG. 4 , utilizing stability studs to secure the distribution grid to a unit of preassembled filter media as shown in  FIG. 3 ; 
           [0043]      FIG. 18  is an exploded perspective view of the primary distribution member and its stability studs shown in  FIG. 17 ; 
           [0044]      FIG. 19  is a cross-sectional perspective view of the primary distribution member and its stability studs shown in  FIG. 17 ; 
           [0045]      FIG. 20  is a cutaway perspective view of the primary distribution member and its stability studs shown in  FIG. 17 ; 
           [0046]      FIG. 21  is an exploded perspective view of a primary distribution member and its elongated stability studs; 
           [0047]      FIG. 22  is a cutaway perspective view of the primary distribution member, shown in  FIG. 21 , utilizing its elongated stability studs to secure the distribution grid to a unit of preassembled filter media; and 
           [0048]      FIG. 23  is a cross-sectional perspective view of the primary distribution member and its elongated stability studs shown in  FIG. 21 . 
       
    
    
     DESCRIPTION 
       [0049]    Various embodiments of the apparatus, systems, and methods of this invention are related to, and improvements of, the mound elimination techniques described in application Ser. Nos. 11/433,794 and 11/543,305, both of which are incorporated herein by reference. Various embodiments of the apparatus, systems, and methods of this invention are also related to, and improvements of, more typical drainfield installations. 
         [0050]    The invention encompasses a number of embodiments that will now be described with reference to the accompanying drawings. The invention may be embodied in many different forms and should not be construed as limited to the embodiments illustrated in the drawings and described herein. Those skilled in the art will appreciate that other embodiments of the present invention can be used in other applications, such as the treatment of effluent using low volume treatment techniques. 
         [0051]      FIG. 1  shows a system for treating household effluent, in accordance with the system disclosed in application Ser. No. 11/543,305 (“application Ser. No. &#39;305”). 
         [0052]    Referring to  FIG. 1 , the system described in application Ser. No. &#39;305 comprises a household  12 , a septic tank  15 , a household effluent pipe  16 , a conduit  20 , MEU  932 , a drainage unit  960 , an “S” shaped unit  974 , and a drainfield reserve  976 . Wastewater flows from the household  12  to the septic tank  15  through the underground household effluent pipe  16 . The effluent is initially treated inside the septic tank  15  before flowing out of the septic tank  15 , through the conduit  20 , and into the MEU  932 . (Note that the MEU  932  is referred to as an “MRU,” for “Mound Reduction Unit,” in application Ser. No. &#39;305.) The MEU  932  comprises an MEU housing  933 , one or more perforated pipes  942 , and filter media  944 . The perforated pipe  942  and the filter media  944  are both housed within the MEU housing  933 . The filter media  944  is comprised of a suitable material for filtering effluent, such as sand, pea gravel, soil, rock, EPS, or some combination thereof. The filter media  944  fills a large majority of the volume of the MEU housing  933 , leaving space at the top of the housing  933  for the perforated pipe  942 . The perforated pipe  942  is positioned generally horizontally atop the upper surface of the filter media  944 . The conduit  20  connects to the perforated pipe  942  that is housed within the MEU  932 . Effluent flows through the conduit  20  and into the perforated pipe  942 . As the effluent flows along the perforated pipe  942 , the effluent slowly drains out of the pipe  942  onto the filter media  944  beneath. Impurities are left behind in the filter media  944  as the effluent drains down through the filter media  944  toward the bottom of the MEU housing  933 , thereby further treating the effluent. 
         [0053]    Continuing with  FIG. 1 , a drainage unit  960  is positioned generally horizontally below the MEU  932 , but at an angle that allows the effluent to flow through the drainage unit  960  in a direction opposite the inlet to the MEU  932 . The drainage unit  960  functions as a drain to direct the flow of effluent from the MEU  932 . The drainage unit  960  comprises a discharge pipe  962  and a generally rectangular grated culvert  964 . The grated culvert  964  is attached to the upper surface of the discharge pipe  962  and to the bottom surface of the MEU housing  933 . The distal end of the discharge pipe  962  connects to an “S” shaped unit  974 . The “S” shaped unit  974  is a pipe that is formed in an “S” shape. The “S” shaped unit  974  is positioned so that gravity will keep effluent flowing through the “S” shaped unit  974  in a direction opposite the inlet to the MEU  932 . The distal end of the “S” shaped unit  974  feeds into a drainfield reserve  976 . Effluent drains from the MEU  932  into the drainage unit  960 . The effluent then flows through the drainage unit  960  into and through the “S” shaped unit  974  and into the drainfield reserve  976 . Once in the drainfield reserve  976 , the cleansed effluent slowly filters down through the soil, eventually reaching the water table. In some systems, a distribution/filtration subsystem is interposed between the septic tank  15  and the MEU  932 . In these systems, the distribution/filtration subsystem performs some initial treatment of the effluent flowing from the septic tank  15  to remove portions of biomass, bacteria, and the like. 
         [0054]      FIG. 2  shows a preferred embodiment in which a distribution grid  10 , in accordance with the present invention, is used in conjunction with a system like an MEU  932  that employs traditional filter media  944  to treat wastewater such as household effluent. 
         [0055]    Referring to  FIG. 2 , an MEU  932  comprises a distribution grid  10 , an MEU housing  933 , and traditional filter media  944 . The filter media  944  is comprised of a suitable material for filtering effluent, such as sand, pea gravel, soil, rock, EPS, or some combination thereof. The filter media  944  fills a large majority of the volume of the MEU housing  933 , leaving space at the top of the housing  933  for a distribution grid  10 . The distribution grid  10  is positioned generally horizontally atop the upper surface of the filter media  944 , with the distribution grid  10  spanning the upper surface of the filter media  944 . A conduit  20  connects to the distribution grid  10  that is housed within the MEU housing  933 . (See  FIGS. 4 and 5  for details.) Effluent flows through the conduit  20  into the distribution grid  10 . Once inside the distribution grid  10 , the effluent continues to flow throughout the span of the distribution grid  10 , draining out through perforations  46 ,  56  (see  FIGS. 6 and 18 ) in the distribution grid  10  onto the filter media  944  beneath. Impurities are left behind in the filter media  944  as the effluent drains down through the media  944  toward the bottom of the MEU housing  933 . When the effluent reaches the bottom of the MEU housing  933 , it drains into a drainage unit  960  (not shown, see  FIG. 1 ). The effluent then flows through the drainage unit  960  and into and through other elements of the system until the cleansed effluent eventually reaches the water table, as described earlier in  FIG. 1 . 
         [0056]    Regarding  FIG. 2 , the distribution grid  10  is constructed with a flat bottom surface so as to remain relatively stable atop the filter media  944 . (See, for example,  FIGS. 12 and 13 .) The distribution grid  10  is optionally anchored atop the filter media  944  using studs  70 ,  90 . (See, for example,  FIGS. 17 ,  19 ,  20 ,  22 , and  23 ). 
         [0057]      FIGS. 3-6  and  17 - 23  show another preferred embodiment in which a distribution grid  10 , in accordance with the present invention, is used in conjunction with a system like an MEU  932  that employs preassembled filter media  30  to treat wastewater such as household effluent. (See  FIG. 3 .) The present embodiment envisions the preassembled filter media  30  to be like the preassembled EPS-netted cylinders  30 ′ disclosed in U.S. Pat. No. 5,015,123 (“U.S. Pat. No. &#39;123”), incorporated here by reference. (In U.S. Pat. No. &#39;123, the preassembled EPS-netted cylinders are identified by reference number “ 30 ,” described and illustrated in  FIG. 3 , and additionally shown in  FIGS. 4A-4C ,  5 , and  6 ). Application Ser. No. &#39;305 identifies an alternate construction of the MEU  932  in which four courses of stacked preassembled EPS-netted cylinders  30 ′ are used. (This version of the MEU  932  is shown in FIG. 12 of application Ser. No. &#39;305.) 
         [0058]    Although the present preferred embodiment envisions an MEU  932  that employs this configuration of EPS-netted cylinders  30 ′ (see  FIG. 3 ), it is to be recognized that alternate embodiments envision an MEU  932  employing other configurations of EPS-netted cylinders  30 ′. For example, an MEU  932  can house more than four courses of stacked EPS-netted cylinders  30 ′ or fewer than four courses of cylinders  30 ′, or even just one course of cylinders  30 ′. An alternate embodiment also envisions an MEU  932  using preassembled filter media  30  like the preassembled EPS-filled paper cylinders  30 ″ shown in  FIG. 15 . Another alternate embodiment envisions an MEU  932  using preassembled filter media  30  like the rectangular, preassembled, EPS-filled paper bags  30 ′″ shown in  FIG. 16 . Still another alternate embodiment envisions an MEU  932  using preassembled filter media  30  like the rectangular, preassembled, EPS-netted bags mentioned in  FIG. 16 . 
         [0059]    Referring to  FIG. 3 , an MEU  932  comprises a distribution grid  10 , an MEU housing  933 , and a plurality of preassembled EPS-netted cylinders  30 ′. The MEU housing  933  contains four courses of stacked preassembled EPS-netted cylinders  30 ′. (This configuration is also shown in FIG. 12 of application Ser. No. &#39;305.) The EPS-netted cylinders  30 ′ fill a large majority of the volume of the MEU housing  933 , leaving space at the top of the housing  933  for the distribution grid  10 . The EPS-netted cylinders  30 ′ are used to filter effluent and serve as an alternative to traditional filter media  944  (see  FIG. 2 ). The distribution grid  10  is positioned generally horizontally atop the upper surface of a topmost course of the EPS-netted cylinders  30 ′. The distribution grid  10  spans the upper surface of this topmost course of cylinders  30 ′. A conduit  20  connects to the distribution grid  10  that is housed within the MEU housing  933 . (See  FIGS. 4 and 5  for details.) Effluent flows through the conduit  20  into the distribution grid  10 . Once inside the distribution grid  10 , the effluent continues to flow throughout the span of the distribution grid  10 , draining out of perforations  46 ,  56  (see  FIGS. 6 and 18 ) in the distribution grid  10  onto the EPS-netted cylinders  30 ′ beneath. Impurities are left behind in the EPS-netted cylinders  30 ′ as the effluent drains down through the cylinders  30 ′ toward the bottom of the MEU housing  933 . When the effluent reaches the bottom of the MEU housing  933 , the effluent drains into a drainage unit  960 . The effluent then flows through the drainage unit  960  and into and through other elements of the system until the cleansed effluent eventually reaches the water table, as described earlier in  FIG. 1 . 
         [0060]    Referring to  FIGS. 4 and 5 , a distribution grid  10  comprises a primary distribution member  40 , a plurality of lateral distribution arms  50 , and a pipe adaptor  60 . A conduit  20  connects to the distribution grid  10  by way of the pipe adaptor  60 . The pipe adaptor  60  comprises a connector end  62  and a base end  64 . A connector end  62  of the pipe adaptor  60  connects to a proximal end of the conduit  20  while a base end  64  of the pipe adaptor  60  fits onto a front end of the primary distribution member  40  nearest the conduit  20 . The lateral distribution arms  50  are connected to the longitudinal sides of the distribution member  40 . Some number of the lateral distribution arms  50  are connected to one side of the member  40  with the remaining arms  50  connected to the opposing side of the member  40 . The distribution arms  50  are oriented laterally to the distribution member  40  and lie in the same plane. (Note that it is conceivable that in an alternate embodiment the lateral distribution arms  50  will be connected to only one side of the distribution member  40 .) The conduit  20  conveys effluent from a septic tank  15  (see  FIG. 2 ) into the primary distribution member  40 . From there, the effluent flows throughout the distribution member  40  and into the connected lateral distribution arms  50 . The effluent drains out through perforations  46 ,  56  (see  FIGS. 6 and 18 ) in both the bottom surface of the primary distribution member  40  and the bottom surfaces of the lateral distribution arms  50  onto the preassembled EPS-netted cylinders  30 ′ (see  FIG. 4 ) beneath. Effluent continues to drain downward through each course of EPS-netted cylinders  30 ′ until it reaches the bottom of the MEU housing  933 . (See  FIG. 3 .) In this way, the distribution grid  10  distributes effluent over the EPS-netted cylinders  30 ′, thereby providing for efficient cleansing of the effluent. 
         [0061]    Still referring to  FIGS. 4 and 5 , the present embodiment envisions three lateral distribution arms  50  extending from a first longitudinal side of the distribution member  40  and two lateral distribution arms  50  extending from a second opposing longitudinal side of the distribution member  40 . The three distribution arms  50  on the first side of the distribution member  40  are positioned generally equidistant from one another, with the three arms  50  being spaced along a majority of the length of the first side of the member  40  and the middle of the three arms  50  positioned generally in the center of the first side of the distribution member  40 . A first lateral distribution arm  50  on the second side of the primary distribution member  40  is positioned across from the approximate center of the area that appears between the middle of the three arms  50  on the opposing first side of the member  40  and the arm  50  nearest the pipe adaptor  60  on the opposing first side of the member  40 . The second lateral distribution arm  50  on the second side of the primary distribution member  40  is positioned across from the approximate center of the area that appears between the middle of the three arms  50  on the opposing first side of the member  40  and the arm  50  furthest from the pipe adaptor  60  on the opposing first side of the member  40 . The lateral distribution arms  50  are connected to the distribution member  40  by snapping the distribution arms  50  into the longitudinal sides of the distribution member  40 . Alternate embodiments contemplate different methods for connecting the distribution arms  50  to the primary distribution member  40 . 
         [0062]    Regarding  FIGS. 4 and 5 , alternate embodiments envision a greater or fewer number of distribution arms  50  connected to a distribution member  40 , and in a different arrangement. For example, a primary distribution member  40  might have three lateral distribution arms  50  connected to each longitudinal side of the distribution member  40 , with the arms  50  in each pair of opposing distribution arms  50  positioned directly across from each other. Another alternate embodiment envisions a distribution member  40  with no lateral distribution arms  50  connected to the primary distribution member  40 . 
         [0063]    Referring now to  FIG. 4 , a distribution grid  10  is positioned generally horizontally atop preassembled EPS-netted cylinders  30 ′. A primary distribution member  40  of the distribution grid  10  resides directly atop one of the EPS-netted cylinders  30 ′ so that the bottom surface of the primary distribution member  40  is adjacent to the upper surface of the EPS-netted cylinder  30 ′. The bottom surface of the distribution member  40  is contoured in a concave shape that approximates the curvature of the outer surface of the EPS-netted cylinder  30 ′. (See particularly  FIGS. 17 and 19 .) This permits the primary distribution member  40  to reside atop the EPS-netted cylinder  30 ′ in a relatively stable manner. Alternate embodiments envision a primary distribution member  40  with a generally flat bottom surface so as to reside in a relatively stable manner atop types of filter media  30 ,  944  that have a generally flat upper surface. (See, for example,  FIGS. 12 and 13 .) The primary distribution member  40  is the same general length as the EPS-netted cylinder  30 ′ atop which the member  40  resides and, given that the distribution member  40  is contoured to reside atop the cylinder  30 ′ in a relatively stable manner, the distribution member  40  is approximately the same width as the EPS-netted cylinder  30 ′ as well. 
         [0064]    Regarding  FIG. 4 , in alternate embodiments the shape and dimensions of the primary distribution member  40  will be dictated, in part, by the type of filter media  30 ,  944  with which it is used. Regarding preassembled filter media  30 , the shapes and dimensions of the primary distribution member  40  will also be dictated, in part, by the dimensions of the filter media  30 . (Note that the shape and dimensions of a pipe adaptor  60  and of lateral distribution arms  50  will, themselves, be dictated in part by the shape and dimensions of the primary distribution member  40  so as to ensure that the entire distribution grid  10  is capable of working as a functional unit). 
         [0065]    Referring to  FIG. 18 , the bottom surface of a primary distribution member  40  contains a plurality of perforations  46 . As effluent flows through the distribution member  40 , the effluent drains out of the perforations  46  onto the EPS-netted cylinders  30 ′ (see  FIG. 4 ) beneath. The effluent that fails to drain out of the perforations  46  in the primary distribution member  40  flows into the connected lateral distribution arms  50  (see  FIG. 4 ). In an alternate embodiment, the primary distribution member  40  does not contain perforations  46 . 
         [0066]    Referring to  FIG. 10 , the bottom surface of a lateral distribution arm  50  contains a plurality of perforations  56 . As effluent flows along the distribution arm  50 , the effluent drains out of the perforations  56  onto the EPS-netted cylinders  30 ′ (see  FIG. 4 ) beneath. It should be noted that the length of lateral distribution arms  50  will be dictated, in part, by the width of the overall surface of an expanse of filter media  30 . (See  FIG. 3 .) In certain applications, the lateral distribution arms  50  might need to be longer to cover filter media  30  with a wider overall expanse. In other applications, the lateral distribution arms might need to be shorter to cover filter media  30  with a narrower overall expanse. 
         [0067]    Referring again to  FIG. 18 , the bottom surface of a primary distribution member  40  contains a plurality of retainer holes  48 . The retainer holes  48  are used for attaching a plurality of stability studs  90  to the bottom surface of the distribution member  40 . The retainer holes  48  are aligned longitudinally along the approximate center of the bottom surface of the primary distribution member  40 . The retainer holes  48  are generally equally spaced one from another. The head of each stability stud  90  snaps into a retainer hole  48 . Once attached, the stability studs  90  remain secured to the bottom surface of the distribution member  40 . In an alternate embodiment, other means for attaching stability studs  90  to the distribution member  40  are envisioned. In another alternate embodiment, the stability studs  90  are part of the primary distribution member  40  itself and not separate elements. In still another alternate embodiment, stability studs  90  are not used with a primary distribution member  40  at all, and the distribution member  40  may or may not contain retainer holes  48 . 
         [0068]    Referring to  FIGS. 17 ,  19 , and  20 , a plurality of stability studs  90  are used to secure a primary distribution member  40  to a preassembled EPS-netted cylinder  30 ′. The heads of the stability studs  90  are attached securely to the bottom surface of the primary distribution member  40 , as described earlier in  FIG. 18 . The stability stud  90  is tapered such that the distal end of each stability stud  90  narrows to somewhat of a point. The pointed, distal end of each stability stud  90  is driven into the upper surface of the EPS-netted cylinder  30 ′, in a generally perpendicular orientation to the upper surface of the cylinder  30 ′, until the bottom surface of the distribution member  40  is brought into contact with the upper surface of the EPS-netted cylinder  30 ′. In this way, the stability studs  90  help to hold the distribution member  40  securely in place. Given the nature of the EPS media that makes up the preassembled EPS-netted cylinder  30 ′, the stability studs  90  drive relatively easily into the EPS-netted cylinder  30 ′. The pointed, distal ends of the stability studs  90  are not long enough to protrude through the bottom of the EPS-netted cylinder  30 ′; consequently, the distal ends of the stability studs  90  remain embedded within the EPS-netted cylinder  30 ′. 
         [0069]    Regarding  FIGS. 17 ,  19 , and  20 , in an alternate embodiment a distribution grid  40  and preassembled filter media  30 , such as EPS-netted cylinders  30 ′, are buried together beneath backfill material. In this embodiment, the additional stability provided by the stability studs  90  can be particularly beneficial. 
         [0070]    Referring to  FIGS. 21-23 , as an alternative to stability studs  90 , elongated stability studs  70  can be used with a primary distribution member  40  to hold the distribution member  40  in place atop a preassembled EPS-netted cylinder  30 ′. 
         [0071]    Referring to  FIG. 21 , retainer holes  48  in the bottom surface of a primary distribution member  40  are used for attaching a plurality of elongated stability studs  70  to the distribution member  40 . The head of each elongated stability stud  70  snaps into a retainer hole  48 . Once attached, the elongated stability studs  70  remain secured to the bottom surface of the distribution member  40 . 
         [0072]    Referring to  FIGS. 22 and 23 , a plurality of elongated stability studs  70  are used to secure a primary distribution member  40  to a preassembled EPS-netted cylinder  30 ′. The heads of the elongated stability studs  70  are attached securely to the bottom surface of the primary distribution member  40 , as shown in  FIG. 21 . The elongated stability stud  70  is tapered such that the distal end of each elongated stability stud  70  narrows to somewhat of a point. The pointed, distal end of each elongated stability stud  70  is driven into the upper surface of the EPS-netted cylinder  30 ′, in a generally perpendicular orientation to the upper surface of the cylinder  30 ′, until the bottom surface of the distribution member  40  is brought into contact with the upper surface of the EPS-netted cylinder  30 ′. In this way, the elongated stability studs  70  help to hold the distribution member  40  securely in place. As with the stability studs  90  described in  FIGS. 17 ,  19 , and  20 , the elongated stability studs  70  drive relatively easily into the EPS-netted cylinder  30 ′. The elongated stability studs  70  are longer than the diameter of the EPS-netted cylinder  30 ′; consequently, the distal ends of the elongated stability studs  70  protrude through the bottom surface of the cylinder  30 ′. A retainer cap  80  attaches snugly over the distal end of each elongated stability stud  70  to secure the stud  70  in place. The present embodiment envisions the retainer cap  80  snapping onto the end of the stud  70 . An alternate embodiment envisions other means for attaching a retainer cap  80  to an elongated stability stud  70 . Another alternate embodiment envisions means for securing the end of an elongated stability stud  70  to an EPS-netted cylinder  30 ′ without the use of a retainer cap  80 . 
         [0073]    Regarding  FIGS. 22 and 23 , as with the stability studs  90  described earlier in  FIGS. 17 ,  19 , and  20 , in an alternate embodiment a distribution grid  40  and preassembled filter media  30 , such as EPS-netted cylinders  30 ′, are buried together beneath backfill material. In this embodiment, the additional stability provided by the elongated stability studs  70  can be particularly beneficial. 
         [0074]      FIGS. 7-9  show alternate configurations in which multiple MEUs  932  are employed to treat wastewater, such as household effluent. Multiple MEUs  932  will need to be employed in some instances where the constraint on available land is great, where the volume of wastewater to be treated is high, or where both factors are extant. The alternate configurations shown in  FIGS. 7-9  are in accord with the preferred embodiment shown in  FIG. 2 , the preferred embodiment shown in  FIGS. 3-6  and  17 - 23 , and all compatible alternate embodiments not specifically shown. 
         [0075]    Referring to  FIG. 7 , an alternate configuration comprises a plurality of incoming conduits  20  and a plurality of MEUs  932 . Each MEU  932  comprises a distribution grid  10 , among other elements. The distribution grid  10 , in turn, comprises a primary distribution member  40 , a plurality of lateral distribution arms  50 , and a pipe adaptor  60 . Each incoming conduit  20  connects to a distribution grid  10  (housed within an MEU  932 ) by way of a pipe adaptor  60 . The pipe adaptor  60  comprises a connector end  62  and a base end  64 . A connector end  62  of a first pipe adaptor  60  connects to a proximal end of a first incoming conduit  20  while a base end  64  of the first pipe adaptor  60  fits onto a front end of a first primary distribution member  40  nearest the incoming conduit  20 . For each subsequent incoming conduit  20 , a connector end  62  of a subsequent pipe adaptor  60  connects to a proximal end of the subsequent conduit  20  while a base end  64  of the subsequent pipe adaptor  60  fits onto a front end of a subsequent primary distribution member  40  nearest the incoming conduit  20 . Connections continue in this way for as many MEUs  932  as are to be connected to unconnected, incoming conduits  20 . 
         [0076]    Referring to  FIG. 8 , another alternate configuration comprises an incoming conduit  20 , a plurality of connector conduits  22 , and a plurality of MEUs  932 . Each MEU  932  comprises a distribution grid  10 , among other elements. The distribution grid  10 , in turn, comprises a primary distribution member  40 , a plurality of lateral distribution arms  50 , and a plurality of pipe adaptors  60 . Note that to connect a first MEU  932  to a second MEU  932  requires that a first distribution grid  10  (housed within the first MEU  932 ) be comprised of two pipe adaptors  60  instead of just one pipe adaptor  60 . A first pipe adaptor  60  will be used to connect the first distribution grid  10  to the incoming conduit  20  while a second pipe adaptor  60  will be used to connect the first distribution grid  10  to a first connector conduit  22 . The first connector conduit  22  will be connected, in turn, to a second distribution grid  10  (housed within the second MEU  932 ) by way of a third pipe adaptor  60 . This third pipe adaptor  60  is an element of the second distribution grid  10 . If the second MEU  932  is to be connected to a third MEU  932 , then a fourth pipe adaptor  60  will be used to connect the second distribution grid  10  to a second connector conduit  22 . The second connector conduit  22  will be connected, in turn, to a third distribution grid  10  (housed within the third MEU  932 ) by way of a fifth pipe adaptor  60 . This fifth pipe adaptor  60  is an element of the third distribution grid  10 . If the third MEU  932  is not to be connected to any other MEUs  932 , then the third distribution grid  10  will be comprised of only this one pipe adaptor  60 , the fifth pipe adaptor  60 . 
         [0077]    Continuing with  FIG. 8 , specific details of how multiple MEUs  932  are connected to one incoming conduit  20  and to each other are now given. A pipe adaptor  60  comprises a connector end  62  and a base end  64 . An incoming conduit  20  connects to a first distribution grid  10  (housed within a first MEU  932 ) by way of a first pipe adaptor  60 . A connector end  62  of the first pipe adaptor  60  connects to a proximal end of the incoming conduit  20  while a base end  64  of the first pipe adaptor  60  fits onto a front end of a first primary distribution member  40  nearest the incoming conduit  20 . A base end  64  of a second pipe adaptor  60  connects to an opposing rear end of the first distribution member  40  while a connector end  62  of the second pipe adaptor  60  connects to a proximal end of a first connector conduit  22 . At this point, one end of the first distribution grid  10  has been connected to the incoming conduit  20  while the opposing end of the first distribution grid  10  has been connected to the first connector conduit  22 . An opposing end of the first connector conduit  22  will now be used to connect to a second distribution grid  10  (housed within a second MEU  932 ) using a second primary distribution member  40  and a third pipe adaptor  60 , both of which are elements of the second distribution grid  10 . A connector end  62  of the third pipe adaptor  60  connects to the opposing end of the first connector conduit  22 . A base end  64  of the third pipe adaptor  60  connects to a front end of the second primary distribution member  40  nearest the incoming conduit  20 . A base end  64  of a fourth pipe adaptor  60  connects to an opposing rear end of the second distribution member  40 . A connector end  62  of the fourth pipe adaptor  60  connects to a proximal end of a second connector conduit  22 . At this point, one end of the second distribution grid  10  has been connected to the first connector conduit  22  while the opposing end of the second distribution grid  10  has been connected to the second connector conduit  22 . An opposing end of the second connector conduit  22  is now ready to be connected to a subsequent distribution grid  10  (housed within a subsequent MEU  932 ). Connections continue in this way for as many subsequent, unconnected MEUs  932  as are to be connected by a connector conduit  22  to a previous connected MEU  932 . 
         [0078]    Still referring to  FIG. 8 , note that the final distribution grid  10  in a series of connected distribution grids  10  will require only one pipe adaptor  60 . This one final pipe adaptor  60  will be used to connect the front end of a final primary distribution member  40  of the final distribution grid  10  to a remaining unconnected end of a final connector conduit  22 . The opposing end of the final connector conduit  22  will have been previously connected to the previous distribution grid  10 . 
         [0079]    Referring to  FIG. 9 , another alternate configuration comprises a plurality of incoming conduits  20 , a plurality of connector conduits  22 , and a plurality of MEUs  932 . Each MEU  932  comprises a distribution grid  10 , among other elements. Each incoming conduit  20  connects to a first MEU  932  by way of a first distribution grid  10  that is housed within the first MEU  932 , as described in  FIG. 7 . For each first MEU  932  connected to an incoming conduit  20 , a second MEU  932  connects to the first MEU  932 , as described in  FIG. 8 . With the connection of the first MEU  932  to the second MEU  932 , a series of connected MEUs  932  has been established. Each subsequent MEU  932  in the series of connected MEUs  932  connects to a previous MEU  932  in the series, terminating with a final MEU  932 , as described in  FIG. 8 . No subsequent MEUs  932  connect to the final MEU  932  in the series. In this way, each incoming conduit  20  is connected to a series of MEUs  932 . Note, however, that in some applications there may be only one MEU  932  connected to a given incoming conduit  20 , rather than a series of connected MEUs  932 . 
         [0080]      FIGS. 10 and 11  show another preferred embodiment in which a drainfield  25 , in accordance with the present invention, is used to treat wastewater such as household effluent. The drainfield  25  comprises a distribution grid  10  and a plurality of preassembled filter media  30 . The present embodiment envisions the preassembled filter media  30  to be like those EPS-filled paper cylinders  30 ″ shown in  FIG. 15 . The present embodiment also envisions the preassembled filter media  30  to be configured as one course of three EPS-filled paper cylinders  30 ″ positioned side by side, with each cylinder  30 ″ parallel to the other cylinders  30 ″. (See  FIG. 11 .) Alternate embodiments employ other configurations of EPS-filled paper cylinders  30 ″, such as two courses of stacked EPS-filled paper cylinders  30 ″ with each course made up of three cylinders  30 ″, or one course of four EPS-filled paper cylinders  30 ″. Another alternate embodiment envisions a distribution grid  10  used in conjunction with preassembled filter media  30  like the EPS-netted cylinders  30 ′ shown in  FIG. 14 . 
         [0081]    Referring to  FIG. 10 , effluent flows from a household  12  into an underground septic tank  15  through an underground household effluent pipe  16 . The effluent is initially treated in the septic tank  15  before flowing out of the septic tank  15 , through a conduit  20 , and into an underground drainfield  25 . In some systems, a distribution/filtration subsystem is interposed between the septic tank  15  and the drainfield  25 . In these systems, the distribution/filtration subsystem performs some initial treatment of the effluent flowing from the septic tank  15  to remove portions of biomass, bacteria, and the like. 
         [0082]    Referring to  FIG. 11 , a drainfield  25  comprises a distribution grid  10  and a plurality of preassembled EPS-filled paper cylinders  30 ″. The present embodiment envisions the drainfield  25  comprising three EPS-filled paper cylinders  30 ″. The three cylinders  30 ″ are positioned side by side, with each cylinder  30 ″ generally parallel to the other two cylinders  30 ″. The distribution grid  10  is positioned generally horizontally atop the EPS-filled paper cylinders  30 ″, with the distribution grid  10  spanning the upper surfaces of the cylinders  30 ″. The distribution grid  10  comprises a primary distribution member  40 , a plurality of lateral distribution arms  50 , and a pipe adaptor  60 . The primary distribution member  40  is positioned atop the middle of the three EPS-filled paper cylinders  30 ″ and optionally secured there using studs  70 ,  90 . (See  FIGS. 17 ,  19 ,  20 ,  22 , and  23 .) A conduit  20  connects to the distribution grid  10  by way of the pipe adaptor  60 . The pipe adaptor  60  comprises a connector end  62  and a base end  64 . The connector end  62  of the pipe adaptor  60  connects to a proximal end of the conduit  20  while a base end  64  of the pipe adaptor  60  fits onto a front end of the primary distribution member  40  nearest the conduit  20 . The present embodiment envisions three lateral distribution arms  50  extending from a first longitudinal side of the distribution member  40  and two lateral distribution arms  50  extending from a second opposing longitudinal side of the member  40 . The lateral distribution arms  50  are configured as described in  FIGS. 4 and 5 . Alternate embodiments envision a greater or fewer number of lateral distribution arms  50  connected to a distribution member  40 , and in a different arrangement. Another alternate embodiment envisions a primary distribution member  40  with no lateral distribution arms  50  connected to the distribution member  40 . 
         [0083]    Continuing with  FIG. 11 , effluent flows through the conduit  20  into the distribution grid  10 . Once inside the distribution grid  10 , the effluent continues to flow throughout the span of the grid  10 , draining out through perforations  46 ,  56  (see  FIGS. 6 and 18 ) in the bottom surface of the primary distribution member  40  and the bottom surfaces of the lateral distribution arms  50  onto the EPS-filled paper cylinders  30 ″ beneath. The EPS-filled paper cylinders  30 ″ contain perforations  36 ″ that accept effluent leaked down onto the paper cylinders  30 ″. Impurities are left behind in the EPS-filled paper cylinders  30 ″ as the effluent drains down through the cylinders  30 ″ toward the soil beneath. Note that in an alternate embodiment, the primary distribution member  40  does not contain perforations  46 . 
         [0084]    Note in addition that the paper skin of the preassembled EPS-filled paper cylinders  30 ″ functions as built-in barrier material. The paper skin of the EPS-filled paper cylinders  30 ″ eliminates the need for inclusion of geotextile fabric or similar products in some drainfield installations. Note further that although  FIGS. 10 and 11  show the use of a single distribution grid  10 , the present preferred embodiment contemplates instances in which multiple distribution grids  10  will be used instead. In such instances, alternate configurations similar to those shown in  FIGS. 7-9  are envisioned. (The major difference between the alternate configurations contemplated by the present preferred embodiment and the alternate configurations shown in  FIGS. 7-9  is, of course, that the present embodiment does not employ MEUs  932  like those shown in  FIGS. 7-9 ). 
         [0085]      FIGS. 12 and 13  show another preferred embodiment in which an underground drainfield  25 ′, in accordance with the present invention, is used to treat wastewater such as household effluent. The underground drainfield  25 ′ comprises a distribution grid  10  and filter media  30 ,  944  that has a generally flat upper surface. The filter media  30 ,  944  can be preassembled filter media  30  or traditional filter media  944 . The present embodiment envisions using one or more rectangular, preassembled, EPS-filled paper bags  30 ′″ like those shown in  FIG. 16 . The number of preassembled, EPS-filled paper bags  30 ′″ required for the drainfield  25 ′ depends upon the dimensions of the EPS-filled paper bags  30 ′″ used.  FIG. 12  shows a first version of the preferred embodiment in which a single preassembled, EPS-filled paper bag  30 ′″ is used in the drainfield  25 ′.  FIG. 13  shows a second version of the preferred embodiment in which three narrower preassembled, EPS-filled paper bags  30 ′″ are used in the drainfield  25 ′. An alternate embodiment envisions a drainfield  25 ′ comprising one or more units of preassembled filter media  30  like the rectangular, preassembled, EPS-netted bags mentioned in  FIG. 16 . Another alternate embodiment envisions a drainfield  25 ′ comprising traditional filter media  944 , such as the filter media  944  shown in  FIG. 2 . 
         [0086]    Referring to  FIG. 12 , an underground drainfield  25 ′ comprises a distribution grid  10  and a preassembled, EPS-filled paper bag  30 ′″. The distribution grid  10  is positioned generally horizontally atop the upper surface of the EPS-filled paper bag  30 ′″, with the distribution grid  10  spanning the upper surface of the EPS-filled paper bag  30 ′″. The distribution grid  10  comprises a primary distribution member  40 , a plurality of lateral distribution arms  50 , and a pipe adaptor  60  (not shown). (See  FIGS. 4 and 5  for details.) The primary distribution member  40  has a generally flat bottom surface, which allows the distribution member  40  to reside atop the preassembled, EPS-filled paper bag  30 ′″ in a relatively stable manner. The primary distribution member  40  is positioned lengthwise atop the EPS-filled paper bag  30 ′″ such that one end of the distribution member  40  is generally aligned with one edge of the EPS-filled paper bag  30 ′″ while the opposing end of the distribution member  40  is generally aligned with the opposing edge of the EPS-filled paper bag  30 ′″ and such that the distribution member  40  is positioned in the approximate center of the EPS-filled paper bag  30 ′″. The primary distribution member  40  is optionally anchored atop the EPS-filled paper bag  30 ′″ using studs  70 ,  90 . (See, for example,  FIGS. 17 ,  19 ,  20 ,  22 , and  23 .) The lateral distribution arms  50  extend from either side of the distribution member  40  and are configured as described in  FIGS. 4 and 5 . The distal end of each distribution arm  50  aligns with a respective edge of the EPS-filled paper bag  30 ′″ such that the distribution grid  10 , as a whole, spans the upper surface of the EPS-filled paper bag  30 ′″. The EPS-filled paper bag  30 ′″ contains perforations  36 ′″ so as to accept effluent leaked down onto the paper bag  30 ′″ through the perforations  46 ,  56  (see  FIGS. 6 and 18 ) in the bottom surface of the primary distribution member  40  and the bottom surfaces of the lateral distribution arms  50 . 
         [0087]    Continuing with  FIG. 12 , effluent flows into the distribution grid  10  from a septic tank  15 . (See, for example,  FIG. 10 .) Once inside the distribution grid  10 , the effluent continues to flow throughout the span of the grid  10 , draining out through perforations  46 ,  56  (see  FIGS. 6 and 18 ) in the distribution grid  10  onto the EPS-filled paper bag  30 ′″ below. Impurities are left behind in the EPS-filled paper bag  30 ′″ as the effluent drains down through the EPS-filled paper bag  30 ′″ toward the soil beneath. 
         [0088]    Regarding  FIG. 12 , in alternate embodiments an underground drainfield  25 ′ comprises a plurality of preassembled, EPS-filled paper bags  30 ′″ of the size shown in  FIG. 12 . In some of these alternate embodiments, EPS-filled paper bags  30 ′″ lie atop one another. In other of these alternate embodiments, the EPS-filled paper bags  30 ′″ lie side by side. In still other of these alternate embodiments, a plurality of EPS-filled paper bags  30 ′″ lie both side by side and atop one another. 
         [0089]      FIG. 13  shows a second version of the present embodiment in which an underground drainfield  25 ′ uses multiple preassembled, EPS-filled paper bags  30 ′″ rather than just one EPS-filled paper bag  30 ′″. Specifically, this version of the present embodiment envisions the drainfield  25 ′ using three EPS-filled paper bags  30 ′″. The three EPS-filled paper bags  30 ′″ are configured as one course of EPS-filled paper bags  30 ′″ positioned side by side, with each EPS-filled paper bag  30 ′″ generally parallel to the other two EPS-filled paper bags  30 ′″. The distribution grid  10  is positioned generally horizontally atop the EPS-filled paper bags  30 ′″, with the distribution grid  10  spanning the upper surfaces of the EPS-filled paper bags  30 ′″. The primary distribution member  40  is positioned atop the middle of the three EPS-filled paper bags  30 ′″. The primary distribution member  40  is optionally anchored to the EPS-filled paper bag  30 ′″ using studs  70 ,  90 . (See  FIGS. 17 ,  19 ,  20 ,  22 , and  23 .) Alternate embodiments employ other configurations of EPS-filled paper bags  30 ′″, such as two courses of stacked EPS-filled paper bags  30 ′″ with each course made up of three EPS-filled paper bags  30 ′″, or one course of four EPS-filled paper bags  30 ′″. 
         [0090]    Note that the present preferred embodiment of an underground drainfield  25 ′ utilizing preassembled EPS-filled paper bags  30 ′″ is well suited to dig out installations wherein a quantity of soil has been excavated and would normally be replaced with soil of better drainage quality. Note in addition that the paper skin of the preassembled EPS-filled paper bags  30 ′″ functions as built-in barrier material. The paper skin of the EPS-filled paper bags  30 ′″ eliminates the need for inclusion of geotextile fabric or similar products in some drainfield installations. Note further that although  FIGS. 12 and 13  show the use of a single distribution grid  10 , the present preferred embodiment contemplates instances in which multiple distribution grids  10  will be used instead. In such instances, alternate configurations similar to those shown in  FIGS. 7-9  are envisioned. (The major difference between the alternate configurations contemplated by the present preferred embodiment and the alternate configurations shown in  FIGS. 7-9  is, of course, that the present embodiment does not employ MEUs  932  like those shown in  FIGS. 7-9 ). 
         [0091]      FIG. 14  shows another preferred embodiment in which a method and apparatus  200  is used to manufacture preassembled EPS-netted cylinders  30 ′, in accordance with the present invention. 
         [0092]    Referring to  FIG. 14 , a volume chamber  230  accepts a supply of aggregate  210  through a secondary gate  220 . The present embodiment envisions the aggregate  210  comprising pieces of EPS media. Alternate embodiments employ other types of aggregate  210 , such as pieces of styrene, Styrofoam, and certain recycled plastics. When the secondary gate  220  opens it creates a space through which aggregate  210  can enter the volume chamber  230 . A predetermined quantity of aggregate  210  is then drawn into the chamber  230 . The predetermined quantity of aggregate  210  may be the quantity required to fill the chamber  230  or the quantity of aggregate  210  may be some lesser amount. At this point, the secondary gate  220  closes and a primary gate  240  opens. When the primary gate  240  opens it creates a space through which the aggregate  210  can be drawn. A blower  250  draws all of the aggregate  210  out of the volume chamber  230  and into a length of sleeve netting  270  (discussed later). The primary gate  240  then closes. At this point, the secondary gate  220  opens again allowing the volume chamber  230  to be refilled with a predetermined quantity of aggregate  210 . 
         [0093]    Continuing with  FIG. 14 , while the primary gate  240  is closed, a length of sleeve netting  270  is drawn along a slide table  260  until the mouth of the sleeve netting  270  is brought into position over the blower exhaust outlet  254 . The mouth of the netting  270  is then secured there. A distal end of the netting  270  is cut at a measured point. This ensures that the netting  270  is of a predetermined length that ensures the predetermined quantity of aggregate  210  will fill the length of netting  270  to a desired level. The distal end of the netting  270  that was just cut is tied off. When the primary gate  240  opens, the blower  250  draws a predetermined quantity of aggregate  210  out of the volume chamber  230  and into the sleeve netting  270 , filling it to the desired level. When the primary gate  240  closes, the mouth of the netting  270  is removed from the blower exhaust outlet  254  and tied off. The filled netting  270  is now a completed preassembled EPS-netted cylinder  30 ′. The EPS-netted cylinder  30 ′ is removed from the slide table  260  and a new length of sleeve netting  270  is drawn forward along the table  260  until the mouth of the sleeve netting  270  is brought into position over the blower exhaust outlet  254 . The next preassembled EPS-netted cylinder  30 ′ is now ready to be constructed. 
         [0094]    Regarding  FIG. 14 , note that preassembled EPS-netted cylinders  30 ′ can be manufactured in various lengths and diameters. The present embodiment envisions manufacturing EPS-netted cylinders  30 ′ with a diameter from eight inches up to twenty inches. Other diameters are also possible.  FIGS. 3 and 4  show a distribution grid  10  used in conjunction with preassembled EPS-netted cylinders  30 ′ like the EPS-netted cylinders  30 ′ manufactured by the present preferred embodiment. 
         [0095]      FIG. 15  shows another preferred embodiment in which a method and apparatus  300  is used to manufacture preassembled EPS-filled paper cylinders  30 ″, in accordance with the present invention. The apparatus  200  described in  FIG. 14  for manufacturing preassembled EPS-netted cylinders  30 ′ is generally the same as the apparatus  300  shown in  FIG. 15 . The method  200  described in  FIG. 14  for manufacturing preassembled EPS-netted cylinders  30 ′ is similar to the method  300  shown in  FIG. 15 . The major difference between the method  200  in  FIG. 14  and the method  300  in  FIG. 15  is that the method  300  shown in  FIG. 15  is used to manufacture preassembled EPS-filled paper cylinders  30 ″ comprising perforated paper tubing  370  filled with EPS aggregate  210 , whereas the method  200  in  FIG. 14  is used to manufacture EPS-netted cylinders  30 ′. 
         [0096]    Referring to  FIG. 15 , the same basic steps are followed here as are described in  FIG. 14 . In the present preferred embodiment, however, when a primary gate  240  is closed, a length of perforated paper tubing  370  is drawn along a slide table  260  until the mouth of the paper tubing  370  is brought into position over a blower exhaust outlet  254 . The mouth of the paper tubing  370  is then secured there. A distal end of the perforated paper tubing  370  is cut at a measured point. This ensures that the paper tubing  370  is of a predetermined length that ensures a predetermined quantity of aggregate  210  will fill the length of paper tubing  370  to a desired level. The distal end of the perforated paper tubing  370  that was just cut is closed up. When the primary gate  240  opens, a blower  250  draws the predetermined quantity of aggregate  210  out of a volume chamber  230  and into the length of perforated paper tubing  370 . The end of the perforated paper tubing  370  is then removed from the blower exhaust outlet  254  and closed up. The filled paper tubing  370  is now a completed preassembled EPS-filled paper cylinder  30 ″. The EPS-filled paper cylinder  30 ″ is removed from a slide table  260  and a new length of perforated paper tubing  370  is drawn forward along the slide table  260  until the mouth of the perforated paper tubing  370  is brought into position over the blower exhaust outlet  254 . The next preassembled EPS-filled paper cylinder  30 ″ is now ready to be constructed. 
         [0097]    Regarding  FIG. 15 , note that preassembled EPS-filled paper cylinders  30 ″ can be manufactured in various lengths and diameters. The present embodiment envisions manufacturing EPS-filled paper cylinders  30 ″ with a diameter from eight inches up to twenty inches. Other diameters are also possible.  FIGS. 10 and 11  show a drainfield  25  comprising a plurality of preassembled EPS-filled paper cylinders  30 ″ like the EPS-filled paper cylinders  30 ″ manufactured by the present preferred embodiment. 
         [0098]      FIG. 16  shows another preferred embodiment in which a method and apparatus  400  is used to manufacture rectangular, preassembled, EPS-filled paper bags  30 ′″, in accordance with the present invention. The apparatus  200  described in  FIG. 14  for manufacturing preassembled EPS-netted cylinders  30 ′ is similar to the apparatus  400  shown in  FIG. 16 . The major difference between the apparatus  200  in  FIG. 14  and the apparatus  400  in  FIG. 16  is that the apparatus  400  shown in  FIG. 16  employs a jig  480 , whereas the apparatus  200  in  FIG. 14  does not. The method  200  described in  FIG. 14  for manufacturing preassembled EPS-netted cylinders  30 ′ is also similar to the method  400  shown in  FIG. 16 . The major difference between the method  200  in  FIG. 14  and the method  400  in  FIG. 16  is that the method  400  shown in  FIG. 16  uses a jig  480  to help manufacture rectangular, preassembled, EPS-filled paper bags  30 ′″ comprising perforated paper-bag material  470  filled with EPS aggregate  210 , whereas the method  200  in  FIG. 14  is used to manufacture EPS-netted cylinders  30 ′ and does not use a jig  480 . 
         [0099]    Referring to  FIG. 16 , the same basic steps are followed here as are described in  FIG. 14 . In the present preferred embodiment, however, when a primary gate  240  is closed, a length of perforated paper-bag material  470  is drawn along a slide table  260  until a proximal end of the paper-bag material  470  is brought into position over a blower exhaust outlet  254 . The proximal end of the paper-bag material  470  is then bunched around the blower exhaust outlet  254  and secured there so that no aggregate  210  can escape the paper-bag material  470  when the aggregate  210  is blown in. The distal end of the perforated paper-bag material  470  is cut at a measured point. This ensures that the paper-bag material  470  is of a predetermined length that ensures a predetermined quantity of aggregate  210  will fill the length of paper-bag material  470  to a desired level. The distal end of the perforated paper-bag material  470  that was just cut is closed up. When the primary gate  240  opens, a blower  250  draws the predetermined quantity of aggregate  210  out of a volume chamber  230  and into the length of perforated paper-bag material  470 . 
         [0100]    Continuing with  FIG. 16 , the perforated paper-bag material  470  is generally rectangular in shape. The perforated paper-bag material  470  is also designed to expand to accommodate the aggregate  210  so as to form a rectangular perforated bag of EPS media. The length of perforated paper-bag material  470  is lain out within a jig  480  so that the perimeter of the rectangular paper-bag material  470  is generally adjacent to the inside perimeter of the jig  480 . The jig  480  is generally rectangular in shape and is positioned horizontally atop the slide table  260 . The rectangular jig  480  surrounds the perimeter of the paper-bag material  470  so as to ensure that the length of perforated paper-bag material  470  maintains a generally rectangular shape when filled with aggregate  210 . Given that the jig  480  bounds the perimeter of the paper-bag material  470 , the length and width of the perforated paper-bag material  470  will be determined by the length and width of the jig  480 . Similarly, each of the four sides of the jig  480  extends upward from the slide table  260 , generally perpendicular to the upper surface of the slide table  260 . The four sides of the jig  480  extend to a height that ensures the jig  480  dictates the height of the perforated paper-bag material  470  when the material  470  is filled with aggregate  210 . In this way, the jig  480  maintains the length, width, and height dimensions of the perforated paper-bag material  470  as each length of the paper-bag material  470  is filled with aggregate  210 . 
         [0101]    Still referring to  FIG. 16 , after the length of perforated paper-bag material  470  has been filled with aggregate  210 , the proximal end of the paper-bag material  470  is removed from the blower exhaust outlet  254  and closed up. The filled perforated paper-bag material  470  is now a completed preassembled EPS-filled paper bag  30 ′″. The paper bag  30 ′″ is removed from the slide table  260 , and a new length of perforated paper-bag material  470  is drawn forward along the table  260  within the jig  480  until a proximal end of the paper-bag material  470  is brought into position over the blower exhaust outlet  254 . The next preassembled EPS-filled paper bag  30 ′″ is now ready to be constructed. 
         [0102]    Regarding  FIG. 16 , note that when new dimensions for preassembled EPS-filled paper bags  30 ′″ are introduced to the manufacturing process, the dimensions of a jig  480  are adjusted to accommodate the new dimensions of the paper bags  30 ′″. The adjustability of the jig  480  provides for the manufacture of EPS-filled paper bags  30 ′″ of various widths, lengths, and heights. In an alternate embodiment, lengths of netting are substituted for lengths of paper-bag material  470 , resulting in the manufacture of preassembled EPS-netted bags that are of a rectangular shape.  FIGS. 12 and 13  show a drainfield  25 ′ comprising one or more rectangular, preassembled, EPS-filled paper bags  30 ′″ like the EPS-filled paper bags  30 ′″ manufactured by the present preferred embodiment. 
         [0103]    The present invention is not necessarily limited to the embodiments herein shown and described. Rather, those skilled in the art will appreciate that numerous modifications, as well as adaptations to particular circumstances, will fall within the scope of the present invention as herein shown and described.