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Septic System Components

The purpose of a septic system is the treatment and disposal of wastewater (effluent) from a household or a business that is unable to access a public sanitary sewage system. Household effluent is about 99.9% liquids, and .01% solids. Many of the substances contained in effluent are pollutants, which are considered to be a hazard to public health if not properly treated.

Below is a comprehensive listing of the septic system components offered by Genest Precast.

Click on any of the topics below to learn more:

Building Sewer
The building sewer is a watertight pipeline that drains the interior wastewater plumbing (via gravity) to the outside septic tank system. Most installers use 4" schedule 40 pipe. In case of a blockage, this piping must be as short as practical to facilitate cleaning, but must extend at least a minimum of 8 foot away from the building.
Septic Tank
A septic tank is a watertight container that is generally made up of concrete. This container provides a place for the primary treatment of wastewater. The raw wastewater is held for a period of one to three days in the tank where it is subjected to a combination of physical, chemical and biological actions, resulting in the conversion of the solid material to liquid and gases. The gases either will escape through the house plumbing vent or will mix with the effluent. After this has occurred, the then clarified liquid will be piped to the disposal field. Some of the solids will remain in the tank as sludge or scum and must be removed periodically to prevent carryover to the disposal field. (See maintaining your system)

Septic tanks must have an inlet and an outlet baffle. These baffles prevent certain materials in the wastewater from entering the disposal area by trapping the substances within the tank. These substances are known as scum and consist of paper, grease, and similar materials that are lighter than the wastewater. The septic tank must have an access cover over each baffle and one in the center of the tank for periodic sludge pumping.

Risers with grouted seams and covers should be considered for placement over all openings to prevent groundwater infiltration into treatment tank openings. Septic tanks should be accessed through the cleanout cover when being pumped to allow the suction hose to reach all sludge accumulations.

Septic Tank Filter
A septic tank filter may be installed at the outlet end of a septic tank to prevent suspended solids from entering the disposal fields. The filter is a slotted cylinder that reduces the size of any solids that may escape the septic tank. The filter is designed to handle the flow of the system it serves and should not result in excess maintenance. (See maintaining your system)

Installing a septic tank filter has the overall benefit of saving money in replacement and maintenance costs as well as providing the owner and the environment with added protection.

Effluent Line
The watertight pipeline that drains the septic tank effluent to the disposal field is called the effluent line. Most installers use 4" SDR 35 pipe. Many disposal fields are gravity fed, but when the disposal area is at a higher elevation than the septic tank, pumping is required. (See Dosing tanks.)
Distribution Box
The distribution box (D-Box) is located in or just before the disposal field. A D-Box is a small tank that has one inlet and multiple outlets that uniformly disperse the flow of the effluent to several lines of a disposal field. A D-Box is very useful when inspecting a failing disposal field to determine possible problems within the system.

In the cold winter months where there is no protective snow cover, freezing can be a problem for the D-Box. Some methods to help prevent freeze-up would be to either provide a layer of insulation over the D-Box cover, or to connect the effluent line to a bottom inlet.
Click Here To View Available Distribution Boxes

Disposal Field
The partially treated wastewater from the septic tank is discharged into the soil at a shallow depth by means of a disposal field (also known as Leachfield). The components of a disposal field are made up of stone, or proprietary leaching devices, that are designed to transmit wastewater into the surrounding soil. The disposal field serves to absorb the effluent load from the septic tank, provide a temporary storage area during periods of large water use, and additionally treat the effluent.
: Stone Bed Disposal Field
A stone bed disposal area acts as an underground retention and final treatment area for effluent. Crushed stone 3/4 to 2 1/2 inches in diameter is used in the construction of a bed. Sizing disposal beds is accomplished by multiplying the design volume of wastewater, (expressed in gallons per day) by the size rating parameter determined by the soil profile classification. This bed provides a void space for the storage of effluent and to allow it to drain into the surrounding soil. The Subsurface Wastewater Disposal Rules require distribution piping within all stone disposal areas (beds and trenches). The purpose is to provide for an even distribution of effluent (as practical) throughout the disposal area(s). We typically sell 4" schedule 20 perforated pipe for distribution piping.
: Proprietary Leaching Devices
A proprietary leaching device is a gravel-less material which is used to create a void area beneath the soil. It replaces the stone and distribution lines in conventional bed or trench disposal areas, although piping is still required for some systems. Each proprietary leaching device is rated by percent equivalence to a stone disposal area system, expressed in square feet. Proprietary leaching devices are pre-manufactured structures of concrete, plastic or other gravel-less material. They are similar to stone beds or trench disposal system, in design, use and function. Installers should refer to the manufacturer's instructions for installation guidance.

The advantages of proprietary leaching devices over the conventional stone bed designs are:

  • reduced area need for installation by 25% to 75%
  • reduced fill volumes required for installation
  • can be removed and reused to create a new system if failure occurs
  • can be installed without stone, an advantage at remote, hard-to-access sites
  • can be configured in terraces, stepping down the natural slope of the land
  • can be manufactured with sufficient strength or designed so that they may be installed under parking lots or traffic-laden areas. (Systems designed for vehicular traffic my have an H-20 lading rate).

The disadvantages of proprietary leaching devices over the conventional stone bed disposal system may be:

  • a higher initial cost
  • requirement for special materials or installation techniques
- Concrete Chambers
Concrete chambers are designed to store effluent discharged from a septic tank. These chambers are rectangular-shaped devices either 4'x8' or 4'x10', which have four sidewalls and a top, but no bottom. ( both manufactured here at Genest Precast) Concrete chambers are quite strong and durable and are relatively heavy, requiring a lift truck (our job here at Genest Precast) to set them in place. The chambers are installed by either using trench or cluster configurations. Effluent then infiltrates into the soil beneath them. The chambers can also allow effluent absorption through sidewall areas, but only when installed in trenches with stone applied to both sidewall areas. These devices must meet the same sitting requirements as stone beds. They must be installed per manufacturer's instructions.
- Plastic Chambers
Plastic chambers perform the same function as concrete chambers but are lighter in weight. Some of these devices have numerous sidewall openings while others depend upon the wicking action of filter fabric. Plastic chambers can be used in either trench or cluster formation. When used in trench configuration, plastic chambers are designed to take advantage of the sidewall area without the use of stone. Due to decreased sidewall contact, more plastic chambers are required if they are to be used in a cluster configuration. Plastic chambers must meet the same sitting requirements as stone bed and must be installed per the manufacturer's specifications.
- Tubing Systems (Enviro-Septic)
Plastic tubing systems are designed to be installed as trenches because they rely heavily upon sidewall area. They have an advantage of being able to follow a contour more closely than other, more rigid systems. Plastic tubing systems must meet the same sitting requirements as stone beds and must be installed as per the manufacturer's directions.

Gravity Flow and Pumping
Once effluent leaves a treatment tank, it must be directed to a disposal area by means of a gravity flow or pump.

The preferred means of directing a small systems effluent to a disposal area is by gravity flow. The disposal area that the effluent is directed towards must be located to the downslope of the septic tank. Gravity flow is cost effective and eliminates the need for a mechanical device that has the potential to breakdown or become inoperative with a power outage. There is however a disadvantage to gravity-flow because it does not provide equal distribution of effluent throughout the entire disposal area.

Effluent pump systems are more expensive than gravity flow systems and require electricity and periodic maintenance. Pumping is usually required when the suitable area for the disposal field is at a higher elevation than the building sewer and does not allow for gravity feed. It can also be required when a system has been placed in or very near an area that has a seasonally high groundwater table. Pumps raise the elevation of wastewater and allow it to enter a disposal area when gravity flow is not possible.

In systems that require pumping, an effluent pump is usually placed on the outlet side or within the septic tank to pump wastewater to the disposal field. Pumping stations should be sited in locations and at elevations which are not subject to either surface or groundwater infiltration. If this is not possible, provisions should be made to prevent infiltration by sealing and/or intercepting and diverting the water source.

A sewage grinder pump or sewage ejector (solids handling pump) can be placed on the building sewer drain to pump raw sewage, which contains solids, to the septic tank. Occasionally, a sewage ejector or grinder pump is installed within the basement of a structure to avoid setback conflicts associated with septic tanks. Care must be taken to utilize a pump, which has been properly sized, to accomplish the task of getting the wastewater to the desired elevation. Selection of the correct pump requires knowledge of head and friction loss calculations (we can help with that here at Genest Precast). Sewage grinder pumps are more costly than an effluent pump. If conditions are right a "solids handling pump" may be substituted for cost-savings.

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