Abstract:
An underground system for distributing and filtering post-septic effluent includes an underground watertight basin containing a filter and conduit connecting a septic tank with the watertight basin for transporting the post-septic effluent into the watertight basin. A discharge pipe connected to the watertight basin transports filtered effluent from the watertight basin into a drainfield reserve for introduction into surrounding natural ground soil.

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
     This application claims priority to Provisional Application Ser. No. 60/714,473 for “Drainage System and Method Using Mount Reduction Techniques” filed on Sep. 6, 2005 and is a continuation-in part of both patent application Ser. No. 10/702,857 filed on Nov. 6, 2003 and application Ser. No. 10/994,809 filed on Nov. 22, 2004 both now abandoned. 
    
    
     BACKGROUND OF THE INVENTION 
     1. Field of the Invention 
     The present invention relates to underground drainfield systems and methods for treating, filtering, cleaning, discharging and recycling septic tank effluent or drainfield water in difficult soil conditions that historically have required an above ground mound system or an intermittent sand filter. 
     2. The Prior Art 
     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 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. 
     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 area of 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. 
     Historically, construction of a drainfield has been expensive, time consuming and inconvenient. Construction usually begins with the excavation of a large rectangular cross section of land by digging multiple trenches at least three feet deep 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. A geotextile fabric or a similar product is placed over the approximately two feet of gravel. Finally, a covering layer of backfill soil is added. This entire process requires transport of large amounts of gravel, backfill soil and piping from a distribution center to the drainfield site. The steps of digging trenches, creating a network of piping and laying different layers of filtering media requires specialized equipment, multiple experienced workers, time, and large amounts of natural resources. 
     In many areas of the country, unique soil conditions require a modified drainfield known as a mound or raised drainfield. In areas with high groundwater, 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. However, above ground mounds often require a mechanical pump to raise effluent from the septic tank above ground to the mound. Second, mounds require transport of additional natural resources to the site. Third, mounds are typically unsightly and greatly reduce the use of the land. Lastly, mounds require a relatively larger area than conventional drainfields and also require routine monitoring and maintenance. 
     For areas with high ground water or impervious soil, one alternative for a mound or raised drainfield is an intermittent sand filter. An intermittent sand filter is a water impermeable basin placed in the ground containing a network of perforated pipes located in a 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. 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. 
     Although intermittent sand filters reduce the need for a mound, improve the appearance of the underground disposal field and allow for better use of the ground, there are several disadvantages. First, intermittent sand filters require transporting large volumes of heavy sand to the drainfield site, which can be very costly. Second, intermittent sand filters require very large cross sections to be effective. For example, a typical two-bedroom home would require a sand filter nineteen by nineteen feet in cross section. Thus, these systems can only work with large acreage households. Third, most intermittent sand filters require a mechanical pump, which results in greater energy and maintenance costs. 
     Apart from intermittent sand filters and mound systems, 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 through one or more commercial vehicles. The good soil is then evenly deposited within the excavated area. A network of perforated piping is assembled and placed on top of 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 an intermittent sand filter, the overall costs, manpower and natural resources required to create a dig out system are significantly greater. 
     There exists a need for an alternative to intermittent sand filters and mound drainfields for efficient treatment, filtration, and distribution of effluent. In addition, there is a need for a filter media that is light weight, portable, inexpensive and allows for increased filtration to decrease the cross sectional size of these systems. Finally, there is a need for such systems to be modular for easy transport to the drainfield site, to allow improved fabrication of these systems, for further reduction in overall costs. 
     SUMMARY OF THE INVENTION 
     This invention is directed to a system and method for treating, filtering, disbursing, discharging and recycling effluent, or any form of wastewater, in difficult soil conditions that historically required either an unpleasant mound or an intermittent sand filter. 
     The present invention comprises a filtration system that includes a sub-system referred to herein as the Mound Reduction Filter Unit (“the MRFU”) and the associated method as the “Mound Reduction Filter Method” (“the MRFM”). In one embodiment, the MRFU is located downstream from a septic tank and is connected to the tank either directly or through an intermediate distribution/filtration sub-system. Aided by gravity, post-septic effluent leaves the septic tank and preferably travels to a distribution sub-system where it is filtered for any remaining sludge, particulates, residue or biomass. Within this post-filtration chamber, effluent is treated for removal of bacteria and pathogens. The effluent then leaves the distribution unit through a second pipeline into the MRFU. Within the MRFU, one or more perforated pipes uniformly distributes the effluent through the MRFU for additional treatment and filtration of any remaining pathogens, bacteria or human waste. In a preferred embodiment, the cleansed effluent then leaves the MRFU through either a slotted linear grate or a series of screened portals into a discharge pipe and then flows to a drainfield reserve. 
     The MRFU comprises a watertight basin that is preferably rectangular, but can be of any shape that provides a sufficient volume of effluent filtration and treatment. The MRFU is made of any resilient material, preferably a lightweight plastic and comprises a bottom, connected sidewalls, and a removable top. The removable top preferably includes a geotextile fabric. Connected at each corner of the bottom side of the removable top are metallic members to permit the MRFU to be opened for maintenance or inspection. 
     The MRFU is filled with filter media that can be any combination of aggregate, soil, sand, gravel, rock, beaded material, or the like. The preferred filter media is variable sized expanded polystyrene (E.P.S.) beads having a diameter on the order of one-eighth inch or less. 
     The MRFU is sized to allow easy transport to a drainfield site via a commercial vehicle. Using a modular construction, several MRFUs can be attached together in parallel or in series depending upon the size and site conditions of the installation. 
     A drainage unit it positioned below the MRFU and functions to transport post-MRFU filtered effluent to the drainfield reserve. The drainage unit comprises two components, a discharge pipe and a culvert. Preferably, the discharge pipe is fabricated from high-density polyethylene (H.D.P.E) or a similar material. 
     Several forms of the culvert are suitable; for example, a rectangular slotted culvert that connects through a slot in the MRFU can be used. Such an arrangement is taught in co-pending application Ser. No. 10/702,857. The slotted portion prevents filter media from escaping the MRFU during effluent transport through the discharge pipe and can be of any known type of grate or a mesh. The top side of the slotted culvert is fitted with the bottom of the MRFU, allowing filtered effluent to flow downward into the discharge pipe. 
     In a second embodiment, one or more grated portals form a linear relationship along the top shaft of the discharge pipe and permit passage of the filtered effluent from the bottom of the MRFU into the discharge pipe while retaining the filter media in the MRFU. These portals are preferably positioned equidistantly along the shaft and in one example are attached on top of a single discharge pipe. Alternatively, a series of component members are attached to linear tubing portions, allowing the use of standard industry H.D.P.E. tubing. These members are either a ninety degree elbow (the initial portion) or a “tee” shaped portion (along the shaft) above which is a grated portal structure. The interface between the drainage unit and MRFU is preferably watertight. 
     From this grated culvert or series of portals, effluent flows downward from the MRFU into the discharge pipe. In another arrangement, the discharge pipe contains a filter media, such as expanded polystyrene (E.P.S.) beads, allowing additional treatment and filtration of effluent. The discharge pipe underneath the MRFU is preferably linear and longer than the total length of the MRFU with a portion of the discharge pipe extending beyond the MRFU in a direction opposite the inlet to the MRFU. The extending portion of the discharge pipe preferably comprises two generally ninety-degree turns, creating an “S”-shaped flow path. To ensure proper flow of effluent via gravity, the end of the “S” shaped portion of the discharge pipe is below the inlet entering the MRFU. This shape should allow flow from the discharge pipe into the drainfield reserve, without need for a mechanical pump. 
     The end portion of the “S” shaped portion of the discharge pipe is connected to one or more reservoir retention chambers, forming a drainfield reserve. These retention chambers are preferably elongated mesh tubes filled with a filter media such as expanded polystyrene aggregate (E.P.S.). A perforated pipe can be placed within the elongated mesh tubes to permit flow to be directed from the discharge pipe throughout the filter media. These elongated mesh tubes are positioned in a generally downward direction from the MRFU allowing gravity to transport effluent along the drainfield reserve. From the drainfield reserve, the effluent then enters the ground water. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       A preferred embodiment of the invention, as well as alternative embodiments, are described by way of example with reference to the accompanying drawings in which: 
         FIG. 1  is a cross sectional schematic view of a septic system according to this invention. 
         FIG. 2  is a top schematic view of the septic system shown in  FIG. 1 . 
         FIG. 3  is a top schematic view showing a septic system that includes three parallel Mound Reduction Filter Units (MRFUs), with accompanying drainage units and drainfield reserves. 
         FIG. 4  is a perspective view of the Mound Reduction Filter Unit (MRFU) and drainage unit sub-systems of the present invention. 
         FIG. 5  is a perspective view of the drainage unit sub-system. 
         FIG. 6  is a perspective view of an alternative embodiment of the drainage unit shown in  FIG. 5 . 
         FIG. 7  and  FIG. 8  are cross-sectional side views of alternative embodiments MRFU-drainage unit constructions. 
     
    
    
     DETAILED DESCRIPTION 
     The present invention will now be described with reference to the accompanying drawings, in which preferred embodiments of the invention are shown. This invention may, however, be embodied in many different forms and should not be construed as limited to the illustrated embodiments shown in the drawings and described in this specification. Rather, these illustrated embodiments are intended to convey the scope of the invention to those skilled in the art. 
     The invention set forth herein provides improved filtration for any effluent or drainage setting, and is not limited to distributing and filtering post-septic tank effluent. For example, the invention can be applied to watershed runoff, collection of rainwater along roads and use in small commercial sites for non-toxic water disposal. Other related uses will be clear to those skilled in the art. However,  FIGS. 1 through 8  illustrate the present invention embodied in a septic system for filtering sewage from a septic tank and, for purposes of illustration includes (i) a combination distribution and filtration sub-system for removing biomass and bacteria, (ii) a sub-system that functions as an alternative to drainfields described herein as a Mount Reduction Filter Unit (“MRFU”), (iii) a drainage unit for collection and transport of post-MRFU effluent, and (iv) a drainfield reserve for final distribution of cleansed effluent into the soil and ground water. 
       FIGS. 1 ,  2   4  and  5  illustrate a preferred embodiment  10  of a filtration system according to this invention. Wastewater flows from a household  12  to a conventional septic tank  14  through a distribution pipe  16  below ground. Within the septic tank  14 , the suspended solids within the wastewater separate according to their density, with heavier solids resting at the tank bottom and lighter solids floating on the surface. Cultures of bacteria are deposited into the septic tank  14  that decompose the solids and other suspensions. Wastewater is usually deposited from the household  12  into the septic tank  14  in periodic intervals throughout the day, most typically in the morning, in the late afternoon and in the evening. Within the period of wastewater deposits, there is a retention time sufficient to allow the cultures to decompose the solids and other suspensions. After this retention time, a subsequent wastewater deposit pushes post-septic effluent from the septic tank  14  into a distribution/filtration sub-system  18  through a post-septic distribution conduit  20 . 
     The distribution/filtration sub-system  18  is preferably rectangular, but could be of any shape known in the art that allows for proper filtration and distribution of effluent. The sub-system  18  preferably comprises three sections: a pre-filtration chamber  22 , a filter  24 , and a post-filtration chamber  26 . Preferably contained within the post-filtration chamber  26  are chlorine tablets  28 . 
     The distribution/filtration sub-system  18  may be fabricated in accordance with the teachings of U.S. Pat. No. 6,277,280, the disclosure of which is incorporated herein by reference. 
     Effluent into the pre-filtration chamber  22  is then separated by the filter  24 . The filter can be a screen, multiple slits throughout the surface of a plane, a perforated grate or a resilient mesh bag filled with expanded polystyrene (E.P.S). Any residual sludge remains in the pre-filtration chamber  22 . The post-filtered effluent then contacts the chlorine tablets  28  for removal of bacteria and further decomposition of any remaining suspensions. During retention times when there is no incoming wastewater into the system, the concentration gradient between the super-chlorinated post-filtered effluent in chamber  26  and the incoming pre-filtered septic effluent causes dissolved chlorine to move across the filter  24  and into the pre-filtration chamber  22 . This further destroys remaining bacteria in the sludge and supports further decomposition of remaining biomass in the sub-system  18 . In the event that the filter  24  becomes clogged due to accumulated sludge, the top of the sub-system  18  can be removed, and the filter can be easily replaced or the sludge can be pumped from chamber  22 . 
     The effluent out of sub-system  18  flows through a post-filtration conduit  30  into a Mount Reduction Filter Unit (MRFU) sub-system, referred to generally with reference numeral  32 . The MRFU  32  is a basin having a bottom  34 , four connected walls including end walls  36 ,  38 , side walls  37 ,  39  and a removable top  40 . The removable top  40  may include means allowing the MRFU  32  to be opened for maintenance or inspection. The conduit  30  is a distance below distribution conduit  20 , allowing effluent to flow through the system  10  without the need for a pump. 
     Effluent from the sub-system  18  flows into the MRFU  32  through an effluent distribution pipe  42 . The distribution pipe  42  can be a single perforated pipe or a network of perforated pipes. Within the MRFU  32 , filter media  44  permits further cleansing of post-filtered effluent from the sub-system  18 . Along the bottom  34  of the MRFU  32  there is one or more slits or openings to allow post-MRFU cleansed effluent to exit the MRFU  34  via a drainage unit as described in greater detail below. 
       FIGS. 2 through 6  better illustrate the MRFU  32 , its internal components and potential arrangements of multiple modular units. The MRFU  32  is preferably rectangular, but can be of any size or shape that provides a sufficient volume to permit complete cleansing and filtration of the effluent from the sub-system  18 . While the sizing of the MRFU  32  can vary, the preferred shape is sufficient to permit the unit to be transported via a flat bed truck or similar commercial vehicle, allowing for uniform fabrication of the MRFU  32  to reduce construction and installation costs. The MRFU  32  can be constructed of any material that permits the unit to be waterproof. Preferred materials for the MRFU  32  include plastic, lined concrete, corrugated material, PVC or any other known water impervious material. Depending upon the size of the household or the household&#39;s generation of wastewater, more than one MRFU  32  can be used. As an example, a parallel arrangement of three units  32  is illustrated in  FIG. 3 . However, the invention also contemplates multiple modular units placed in series or both parallel and in series, depending upon either or both the treatment demands or acreage space constraints. 
     The internal construction of the MRFU unit  32  is illustrated in greater detail in  FIG. 4 , where the walls, top and bottom of the MRFU  32  are shown by dotted lines. The filter media  44  can be any suitable material including but not limited to sand, pea gravel, soil or rock. However, as described above, the preferred filter media  44  for the MRFU  32  is variable sized expanded polystyrene (E.P.S) beads that are one-eighth inch or less in diameter. There may be one or more different layers of filter media within the MRFU  32 . By way of example, three separate layers of filter media  44  are shown in  FIG. 4 , including a top layer of lightweight large polymer aggregate  46 , an intermediate layer of expanded polystyrene  48 , and a lower layer of heavy small-sized polymer aggregate  50 . One advantage of using expanded polystyrene beads  48  is that some particulates in the effluent may have a static charge. 
     Attention is now directed to  FIGS. 1-4 . Positioned through the MRFU  32 , is an effluent distribution network that connects effluent flow to the MRFU  32  from either a sub-system  18  or directly from the septic tank  14 . In one arrangement the effluent distribution network includes a central pipe  42  coupled with a series of evenly spaced lateral perforated pipes coupled to the central pipe  42 . Other shapes and arrangements for the effluent distribution network can be envisioned by those skilled in the art. As shown by flow arrows in  FIG. 4 , the effluent flows into the effluent distribution network through the pipes  42 ,  43  and then downward throughout the filter media and into the drainage unit, referred to generally in  FIG. 4  with reference numeral  60 . 
       FIG. 5  shows one embodiment of the drainage unit  60 , which includes a discharge pipe  62  and a generally rectangular grated culvert  64 . The discharge pipe  62  is preferably rigid and made of high-density polyethylene (H.D.P.E.); however, alternative materials include sheet metal, corrugated material, PVC, lined concrete or any similar material known in the art. The rectangular grated culvert  64  is attached via a watertight seal  66  on top of the rigid discharge pipe  62 , and functions as a drain to filter and direct the flow of effluent from the MRFU  32 . The grated culvert  64  has a preferably grated or mesh top  68 , four enclosing side walls  70 , and an open bottom  72  that forms a watertight seal with the top of the discharge pipe  62 . The grated culvert  64  is preferably made of the same material as the discharge pipe  62 . 
     As shown in  FIGS. 1 ,  2 , and  5 , an “S” shaped unit  74  located at the distal end  63  of the discharge pipe  62  is connected to one or more reservoir retention chambers  76  each of which is coupled with a drainfield reserve  78 . The “S” shaped unit  74  may, for example, comprise of two generally 90 degree turns in the discharge pipe  62 . The “S” shaped unit  74  is positioned below the conduit  30  to allow flow out of the discharge pipe  62  via gravity. The distal end of each “S” shaped unit  74  is then connected to at least one reservoir retention chambers  76 . In a preferred embodiment, each retention chambers  76  comprises a mesh bag filled with expanded polystyrene beads. However, the material within the retention chamber  76  can be any polymer aggregate, pea gravel, rock or related material known in the art. Further, a perforated pipe can be added to the retention chamber  76  for distribution of effluent to a drainfield reserve area adjacent each retention chamber  76 . 
       FIG. 6  illustrates an alternative embodiment for the connection between the bottom  34  of the MRFU  32  and the drainage unit  60 . In this arrangement, the bottom of the MRFU  32  includes two downwardly extending sidewalls  33 ,  35 . The sidewalls are preferably integrally formed with the MRFU  32 . The sidewalls  33 ,  35  connect directly with opening  72  in the discharge pipe  62 . 
       FIG. 7  shows an additional embodiment for the drainage unit. In this alternative arrangement, the drainage unit  80  includes multiple passageways  84  positioned in series along the discharge pipe  82 . One preferred form of such a passageway  84  or system of passages with grates  86  therein. However, one of ordinary skill in the art can envision alternative passageways  84  or shapes for such grated portals. For example, the passageways  84  could be circular, elliptical, square, or any known shape that allows a sufficient cross-sectional area and flow path for transport of effluent to enter the discharge pipe  82 . 
     While the portals may be attached to a single length of discharge pipe as shown in  FIG. 7 , the drainage unit can be constructed of multiple components for assembly on-site, and to further reduce costs, by using commercially available H.D.P.E corrugated tubing. 
     Such an arrangement is shown in  FIG. 8  and described next. 
     There are three main components in the embodiment of  FIG. 8 : (i) a ninety-degree initial member  90  that includes a portal  92  having a grate  94  on the top of the initial member  90 ; (ii) tee shaped secondary members  96  that includes a portal  98  on the top of that member, and portions of HDPE corrugated tubing  98  to connect between these members. Located at the distal end of this multi-component drainage unit is a generally “S” shaped fixture that includes a first ninety-degree “S” portion  100  and a second ninety-degree “S” portion  102 . Between these two portions is a portion of HDPE corrugated tubing  104 . Positioned before the second ninety-degree “S” portion is a final screen  106  to shield any excess particulates, suspensions, or escaped filter media from entering the drainfield reserve  76 . The connections between these multi-component parts, the MRFU  32 , and the reservoir retention chamber  76  should be generally watertight. 
     Also shown in  FIG. 8  is an additional component to the drainfield reserve  76  known as a trough  108  which is an additional tubular mesh bag filled with variable sized polystyrene beads  110  and is positioned just below the reservoir retention chamber  76  at the point where the end of the second ninety-degree “S” portion connects with the beginning of the reservoir retention chamber  76 . The trough  108  assists in distributing post-filtered discharge across the width of the drainfield reserve, as well as prove a buffer or barrier to prevent post-filtered discharge to exist the system mainly at the initial portion of the reservoir retention chamber  76 . 
     From the description of the underground disposal system set forth above, one of ordinary skill can easily envision several methods for using this apparatus for filtering, treating, distributing and cleansing effluent for introduction into the ground soil.