Anatomy of a Septic Drain Field

One of the most important elements of a home septic system is the drain field. Alternatively referred to as the seepage bed, leach field or soil absorption area, the drain field is the final step in the wastewater remediation process. Most state and local authorities enforce strict regulatory requirements on the construction and location of new drain fields and may require homeowners to maintain an alternative drain field location in the event the current field fails or is rendered unusable. Well-positioned and constructed drain fields can last for 20 years or more.

Drain field construction
New drain field projects must usually be approved by local health authorities or county officials before construction can begin. In cases where a permit is not required, inspections may be necessary in order to ensure that the drain field is properly positioned and that it meets local and state standards for environmental protection. The absorption capacity of the soil should be tested as well to determine if it can manage the volume of water expected from the septic system arrangement. Most experts recommend soil percolation rates of less than 60 minutes per inch, but rates of up to 90 minutes per inch may be allowable in some areas. Once the location has been determined, the following steps will take place:

  • The contractor or homeowner will dig parallel trenches in the drain field location. These trenches should not exceed 100 feet in length. Depending on local regulations, each of the trenches should be between 1 and 3 feet in depth and about 18 inches wide.
  • A layer of gravel should be placed at the bottom of the trench to a depth of about 1 foot.
  • Perforated distribution pipes should be connected to the distribution box that leads to the septic tank. These pipes rest atop the gravel already placed in the trenches.
  • The trenches should then be filled with gravel and covered with a fabric barrier to prevent soil from entering the gravel field. Tarpaper is often used for this purpose.
  • The drain field area should then be covered with topsoil and, if desired, seeded with grass or covered with sod.

Wastewater will flow from the septic tank into the distribution box and into the pipes and trenches of the drain field. It will then filter through the gravel and ground below the drain field and eventually return to the water table under the soil.

Drain field maintenance and repair
Most septic system problems occur due to inefficient decomposition by bacteria within the septic tank itself; however, in some cases, drain fields may require maintenance as well. One of the most common reasons for drain field failure is a blockage or broken pipe within the distribution box. This can cause overload in certain parts of the field while leaving other pipes dry and ineffective. Repair or replacement of the distribution box is a relatively low-cost proposition and should be performed immediately if necessary in order to prevent full-scale drain field failure.

By constructing a high-quality drain field, maintaining it properly and reducing its load through the use of aerobic bacterial systems within the septic tank, most homeowners can significantly increase the lifespan of new or existing septic systems.

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