GreenLeach - Enhanced Filtration Systems - Frequently Asked Questions

  What is a GreenLeach Filter? It is an environmentally friendly leaching system product that is very effective in allowing liquid discharged from a septic tank or sewage treatment system to be adsorbed and dispersed into soil. When effluent is discharged to the center core, the liquid leaving the core and sidewalls of the numerous fins passes through a filter fabric. This fabric provides a stable platform for the biological mat to quickly form, thus providing added effluent treatment through the mat and the fabric.  

How is the product shaped and why? GreenLeach Filter is designed as a linear leaching system consisting of a 12” gravel filled center core that runs the length of the trench and 4” wide gravel filled leaching fingers extending off both sides. The fingers are 25” long with 4” of porous sand backfill placed on the outside of the fabric in between each finger. Cardboard is used as a temporary form to hold the fabric-covered fingers in place until construction is completed. The cardboard will degrade in time with moisture and effluent application, leaving the gravel in contact with the filter fabric and sand. The product was designed in this manner to maximize the area for growth of a biological mat (bio mat) while still maintaining an aerobic atmosphere in the sand backfill placed on the outside of the fingers. The resultant product permits more leaching area to be installed in a smaller area, thus saving on system installation.  

Why use so many plastic finger spacers on top? Product stability during installation is a critical factor. The patented spacer and disposable gravel chute system hold the core and fingers rigid during the entire gravel placement and sand backfill process. The leaching fingers do not deform thereby allowing easy spreading of ” gravel to the finger ends and likewise, sand between the fingers. The spreaders can be removed when the product stabilized with gravel in place and some sand spread in between the fingers. The chute is easily removed upon completion of gravel placement.  

Can all GLF units be used beneath parking lots? The GreenLeach Filter units fall into the same category as standard gravel trenches which have been used beneath parking lots for decades so the answer is a definite YES! The 4” diameter PVC pipe is totally encased by the ” stone. Gravel placed inside the form does not compact at all and sand used to backfill the fingers is compacted as part of the installation. Once properly installed, nothing will settle and the 4” diameter PVC distribution pipe remains stable. The distribution pipe will be subjected to heavier than normal loads so use of heavy duty perforated ASTM D3034 SDR 35 pipe is recommended. The CT Public Health Code requires a minimum of 2” of gravel (stone) above the pipe to totally encase the pipe in a protective stone case. The Code also requires a minimum of 6” soil cover above the stone. For parking lots, the minimum recommended cover above the top of the pipe should be increased to a total of 12” of stone, sand & gravel, processed gravel or some combination of the three. The added soil cover reduces the pressure on the distribution pipe and the added wall thickness of the SDR 35 pipe assures the channel remains round. Similar care must be given to the solid distribution pipe used between the GLF and the septic tank. Either specify use of ASTM D 1785 Schedule 40 if no bedding (stone) is to be provided or use the SDR 35 bedded in stone as described above including the 12” stone/soil cover. No cast iron or ductile iron pipe can be used after the septic tank. If small diameter pressure distribution pipe is placed in stone on top of the GLF, there is less concern for crushing due to the increased strength and wall thickness of the small (1-2”) diameter water pressure pipe. Based upon years of experience with all leaching systems, the standard 2” stone cover and 6-8” of additional process cover would be adequate to protect the pipe.  

Can filter fabric be placed beneath the GreenLeach Filter? In environmentally sensitive areas, it may be advisable to add the extra filtering benefit by placement of filter fabric beneath the trench. All new septic systems constructed in soils allow a higher rate of pollutants to escape the system until formation of a stable biological mat (bio mat). The fabric will help form a mat more quickly but will result in a slight reduction in credited effective area (0.4 SF/LF) based upon the CT DPH rating criteria. The 6” depth of select sand fill required beneath every GreenLeach system constructed also provides efficient filtration prior to effluent reaching the natural soils.  

What are some physical differences between the GreenLeach Filter and some other common leaching systems? All leaching systems allow effluent to leach into the surrounding soils using various media and methods. Many hollow chambered structures use direct soil application, may use gravel backfill, employ filter fabric covering or have slotted/perforated sidewalls to facilitate liquid transfer to the soil. Common gravel trenches use clean gravel to provide voids for effluent storage and are constructed with gravel directly contacting the soil on the bottom and sides. Some specialty products use styrene or rubber tire chips to imitate gravel. The GreenLeach Filter is slightly different in that it uses 4 inch wide filter fabric covered fingers that are specifically backfilled on the outside with washed concrete sand (or naturally sandy, permeable soils) and the inch gravel placed on the inside of the fingers provides structure to keep the fabric in place, prevents the fingers from collapsing during construction, protects the distribution pipe and distributes surface loads placed on the system. The gravel provides internal liquid storage to assist with peak flow storage and distribution.  

How does the GreenLeach Filter stack up against other systems? The GLF excels in providing effluent contact area between the fabric/gravel product and the sand backfill on the sides and bottom. The GLF provides wetted contact area between the sand and filter fabric area as shown below: (NOTE-THIS IS PHYSICAL CONTACT AREA BETWEEN EFFLUENT AND SURROUNDING SOIL ONLY)/b>

               GLF 12-62 17.6 square feet per lineal foot of product
               GLF 15-62 21.15   "
               GLF 18-62 24.8    "
               GLF 21-62 28.45   "
               GLF 24-62 32.0    "
               GLF 27-62 34.75   "
               GLF 30-62 38.3    "
               GLF 33-62 41.95   "
               GLF 36-62 45.7    "

The Infiltrator (trade mark) Equalizer (16” high x 34” wide) chamber provides about 6.0 square feet per lineal foot contact area (bottom and sides) with the soil when placed in a trench.

A standard 3-foot wide, 18’ deep gravel trench with 12” of gravel beneath the pipe provides about 5.0 square feet per lineal foot contact area with the soil.

A 48” wide, 12” high concrete gallery installed in a 6’ wide trench using 12” of gravel on the gallery sides provides about 7.5 square feet per lineal foot contact area with the soil.

Comparison with these three and many other leaching systems clearly show the advantages to using the GreenLeach Filter as a means to provide effective leaching area in a compact space. Do the math with any other system and you too will see how effective the GLF actually is.


Why do the CT ratings and actual soil contact areas shown above differ? The CT State Health Department uses a mathematical formula to give credit to all types of leaching products and takes into consideration the bottom and vertical leaching interfaces as well as the type of effluent-soil contact (direct as with chamber bottoms, gravel, fabric, etc.). They also include a safety factor which is why the “wetted perimeter” of a gravel trench with a 3’ wide bottom and 12” below the invert actually has 6 square feet of contact area yet is rated at only 3 square feet per linear foot.  

What does the difference in square footage contact area mean to an engineer or installer who is designing a septic system to serve a 4-bedroom home? If the State, County or Local Health Department regulations called for installation of 2 rows, 85 feet long (170’ total) of a hollow plastic chambered system, 16” high, 34” wide, then replacement by the GreenLeach Filter would substantially reduce the length of trench installation depending upon the height of GLF used. Using the GLF 18-62 (18” high), about 41 feet of product would be necessary to provide the same soil contact area. In CT where safety factors are incorporated in product ratings and variables are used for various soil interface types, the leaching product rating formula would equate the 150’ plastic chamber system to about 60.3 feet thereby significantly reducing the area required for system installation. This is a critical factor for repairs on small lots or on properties that may contain only pockets of suitable soil. If site conditions were not restricted by groundwater, ledge rock, hydraulic limitations or impervious soil conditions, use of the GLF 36-62 could further reduce trench lengths down to 33 feet of product using the conservative CT rating system. The GLF does require more labor during installation but the rewards are very obvious.

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