How does a Drain Field work? | Working of Leach Field

What is a Drain Field?

A drain field is a network of underground perforated pipes adjacent to the septic tank. When the liquid wastewater leaves the septic tank, it is transferred to the drain field, which removes the impurities from the wastewater and seeps it into the ground.

The drain field is also known as a leach field, leach drain, sewage area, or septic tank drain area.

drain field

It has multiple discharge perforated pipes, and soil is used to cover the porous materials (usually gravel) to prevent animals from reaching the sewage distributed and layered in these trenches.

The primary design contains the hydraulics of the volume of effluent to be treated and catabolic for a long time BOD of that effluent. Areas set separately for septic tank leach fields are sometimes referred to as septic tank reservation areas (SRAs).

Working of Drain Field

The main function of the drain field or leach field is to collect the liquid wastewater from the septic tank and seep this liquid waste into the ground.

Drain field working

A drain field works in the following way:

  • First of all, the waste flows from your sump pit or toilet into the septic tank.
  • This septic tank contains biological bacteria that break down the waste.
  • The liquid waste such as grease, oils, and fats float to the tank surface while solid wastes (such as debris) sit down at the septic tank base and convert into sludge.
  • As the waste reaches a specific level, the septic pump activates, and it discharges the liquid waste into the drain pipes.
  • The septic tank has a septic filter just before the drain pipe at the outlet. This filter stops the solid waste from going into the drain pipes.
  • After passing through the drain pipes, the liquid waste enters the leach field, where it seeps into the ground below, where the soil naturally filters it.
  • The solid waste still remains at the tank bottom. A septic tank pumping method is used to remove this solid waste.

Symptoms of Leach Field Failure

The proper maintenance of the leach field is very important for its proper working. There are multiple signs of a bad leach field, but the most common signs are given below:

  1. Bad Odor: If you observe an unpleasant odor in your building, this may be due to a bad drain field. When liquid wastewater doesn’t properly discharge from the septic tank to the drain area, it collects on the soil surface. Due to this collection, an unpleasant and noticeable dirty odor generates.
  2. Drainage Problems: If you have a frequent clog or backflow of wastewater in your house, you may have discharge issues in the drain area of your system.
  3. Backflow of the Sewage: If your toilet or sump pit sewage doesn’t properly transfer into the septic tank and backflows, it means your septic tank has been full, and your wastewater is not draining into the leach field. This problem occurs due to the clogged drainage pipes that transfer liquid waste from the septic tank to the leach field.
  4. Standing Water: Unnecessary buildup of sewage can result in stagnant If so, you may see an inexplicable puddle in your yard. In such a condition, immediately open your leach field and inspect it. If there is a severe issue, call the specialist to fix it.
  5. Increased Plant Growth: If you observe a fat growth of weeds or grass near your drainage area, it means your drain field is leaking more quickly than normal. The waste nutrients can promote plant growth.

Design of Drain Field

Generally, the septic drain field has 16 to 30 inches in depth, and the maximum soil cover on the drain area is 36 inches, or 2 to 5 feet deep, according to the USDA.

Approximately 15 cm of clean rock is used to fill up each trench bottom, and a perforated pipe is placed on it. Sometimes, a few extra rocks use to cover the pipelines.

leach field design

Lay a layer of geotextile fabric on top of the rock layer to stop small atoms from clogging the pipes. The last layer of the topsoil or sand uses to cover the geotextile and fills the trench up to the ground level. The pipe must be laid at least 15 cm below the surface to stop wastewater from reaching the surface.

The length of the trench should not be more than 20 m, with a minimum distance of 1-2 m. The leachate must be at a minimum distance of 30 meters from the drinking water source to avoid contamination.

The seepage water must be introduced in such a way that it does not interfere with future sewer connections. Collection techniques upstream of leachate (e.g., septic tank) should be fitted with a sewer connection to allow conversion to occur with minimal disruption when the leachate needs to be replaced.

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Can You Repair a Septic Drain Field?

The repairing process of a clogged drain field is very easy. However, many catastrophic issues may appear in the leach field, such as the growth of bacterial mats. Proper care and maintenance of the septic drain area are very important for its proper working.  

Follow the below-given tips for the proper operation of the septic drain field.

  • Do not pour ammonia, paint, bleach, chemicals, or grease into your septic tank.
  • Avoid washing anything other than body fluids and bath towels.
  • Use your waste-handling equipment with care (or don’t use it at all).
  • Limit laundry to once a day to increase water intake. This process is compulsory to lower the load on the leach field.
  • Avoid parking your car, building structures, or heavy objects in the drain area.
  • Don’t discharge excessive snow or rain into the septic drain field.
  • Follow the schedule for regular septic tank pumping, typically every 3 to 5 years.
  • Work on annual inspection and symptomatic services for the proper septic tank operation.

Advantages of Drain Field

  1. The septic drain field has a long service life.
  2. The drain field may also be used for the mutual treatment of greywater and blackwater.
  3. They require very low maintenance.
  4. They can operate in almost all climate conditions (not when the ground freezes).
  5. These systems have low operational costs.
  6. They have low capital costs.

Disadvantages of Drain Field

  1. The leach field has complex construction.
  2. You need an expert for its construction.
  3. All materials and parts used for the septic drain field may not be locally accessible.
  4. The construction of a leach field requires a large area.
  5. This system requires proper care for proper operation.
  6. It needs primary treatment to stop clogging issues.

FAQ Section

What is a Leach Field?

Leach Field

An area in which liquid waste of the septic tank is accumulated is known as a leach field. The liquid waste flows from the septic tank to the leach field via drain pipes. 

What are the signs of a bad drain field?

  • Clogging of the drain pipes.
  • Backflow of the waste from the drain field to the septic tank.
  • Standing water or wet, mushy grass over the leach field.
  • No discharge of the wastewater from the septic tank to the leach field.
  • Slow draining of the wastewater.
  • An unpleasant odor comes out from the leach field, drain pipes, or septic tank.
  • There is water or wet grass in the leach field.
  • Toilet flushing problems such as no flushing, slow flush, or low flushing pressure.

How long does a leach field last?

The service life of the leach field depends on its maintenance and care. A properly maintain leach field has a service life of up to 50 years

What is the difference between a septic tank and a leach field?

A septic tank uses to store liquid and solid waste. The solid waste sits at the bottom of the septic tank while the liquid waste is discharged into the leach field through drain pipes. A leach field is an area where liquid waste accumulates and seeps into the ground. The ground soil naturally filters the waste liquid. 

What is the average cost of a drain field?

The replacement cost of the leach field or drain field varies according to the area you live, the contractor rate, and other factors. The average replacement cost of the drain field is from $4,900 to $21,000.

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1 thought on “How does a Drain Field work? | Working of Leach Field”

  1. What caught my attention was when you said that an unpleasant and noticeable dirty odor is generated if the liquid wastewater doesn’t properly discharge from the septic tank to the drain area. This is something that I will share with my parents so they can be convinced to hire a leach field repair company within the day. I visited them yesterday afternoon, and I noticed that their house is filled with foul odors similar to a rotting egg.


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