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Leach Field / Septic Drain Field Everything You Need To Know

A leach field or septic drain field is the final processing step or sewage treatment in a septic system. Also known as a drain field, leech field or absorption field. The leach field as it is most commonly known as is a network of underground pipes containing many small holes to allow the wastewater to be distributed into the surrounding soil.

In this article, we will tell you in plain English; what a leach field is, how it works how to spot problems as well ask answer the most frequently asked drain field questions.

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If you're having problems with your leach field, it is most likely starting in your septic tank.
Here are our most popular articles to help you out:

  1. What to put in your septic tank to BREAK DOWN solids & grease
  2. What to do AFTER your septic tank is pumped
  3. Best monthly septic tank treatment to AVOID system failure & Save $$$

 

What is a leach field?

A leach field is one of the major components that make up a septic system. Located under the ground, a network of small corrugated pipes are connected to the septic tank via the outlet pipe and a distribution box or manifold that handles the pressure distribution by allocating wastewater into several absorption trenches in the yard.

Also called a drain field, the main job of the drain field is to remove contaminants like harmful coliform bacteria from septic tank effluent via perforated pipes or corrugated drainage pipe called leach lines that soaks the surrounding soil. Using the soil bacteria to naturally remove nasties before they reach the water table or groundwater.

To ensure that the maximum amount of treated septic effluent can be processed below the ground surface, the perforated pipes of the leach lines are usually laid in drain field trenches that often consist of gravel covered with soil to maximise the oxygen and drainage potential and avoid groundwater runoff. When a septic system is installed the area set aside for the drain field is often called the septic reserve area or SRA. Many counties will require a secondary SRA be available should there be a failure in the leach field pipes or a clogged leach field or a failed leach field. In this case, there is a secondary area to dig new leach pits and run drain line pipes.

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Signs of leach field problems

One of the main causes of a clogged leach field is not having your septic tank pumped on a regular basis to remove solid waste. If grease or solid waste enter the outlet pipe and into your leach lines or perforated piping, this can clog up the lines. As the leach field is located under ground, this makes it hard to find the problem.

If your leach field is not functioning properly then you will most likely already be experiencing some of these leach field problems:

  • When pipes are turned on, they gurgle.
  • Slow-moving drains.
  • Wastewater backing up into the septic tank and potentially the house
  • Problems with toilets flushing slowly or not flushing at all
  • Sewage odors coming from drains, the septic tank or leach fields
  • Septic tank overflowing or standing water near the septic tank or leach field

Drain field repair or replacement?

The question is can you repair a leach field if it becomes clogged with solid waste or algae, or do you need to replace the entire septic system? A leach field is designed to last 15 to 20 years if treated well.

How to prevent a leach field from failing

Prevention is always better than the cure and when it comes to septic system repairs, it is also much cheaper.

  • Use a monthly septic tank treatment to break down solids and reduce scum
  • Don't put harmful chemicals down the drain or toilet such as bleach or ammonia-based cleaners
  • Never put motor oil, paint or grease down the household plumbing
  • Only flush human waste and approved toilet paper down the toilet
  • Avoid using a garbage disposal, if you do use it infrequently
  • Don't do laundry loads back to back, spread them out to limit wastewater going into septic tanks
  • Never drive or park vehicles or heavy equipment on your leach field
  • Ensure you know when your next septic tank pump is due
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Septic tank drain field layout and leach field design

Septic tank drain field layout is a key part of installing a septic system. If you are looking to have a septic tank replaced or installed at your house call 888-985-3072 to get a quote and talk through a septic system plan or septic system designs that suit your local regulations and property.

Before you get a septic system design in the US your local health department usually requires a percolation test (also known as a "perc" test) to determine if drain field soil is suitable for receiving sewage tank effluent. Percolation tests are used to determine how quickly clean septic systems water is transported into the ground via a disposal trench.

The purpose of soil testing using the perc test and the reason it is required by a local health department is to make sure the soil is absorptive enough for septic tank effluent to flow away from the drain field while ensuring the particles are fine enough to filter out pathogens, harmful coliform bacteria and viruses before they can make their way to the surface or to groundwater. Course mediums such as sand and gravel may lead to wastewater being carried away from the drain field before diseases are eradicated. Silt- or clay-based soils efficiently remove germs but allow minimal wastewater flow rates.

 

Where is a leach field located?

A typical question is where is my leach field located. They are generally found in a big, flat, and open part of your yard. They may have anywhere from one to three feet of earth on top, with trenches ranging in depth from 18 to 36 inches and width from one to three feet and up to 33 yards long. The typical distance between leach field pipes is around six feet.

 

Mound system septic drainage

Mound systems are an option in areas of shallow soil depth, high groundwater, or shallow bedrock. The constructed sand mound contains a drainfield trench. Effluent from the septic tank flows to a pump chamber where it is pumped to the mound in prescribed doses.

 

Frequently asked questions

How deep is a leach field

A leach field may have anywhere from 1 to 3 feet of earth on top, with gravel filled trenches ranging in depth from 18 to 36 inches.

 

How long does a septic drain field last?

How long a leach field will last will depend on how old the septic tank is and how well it has been looked after. Most leach fields will last 15-20 years if looked after well.

 

Can a leach field be restored?

That will depend on the problem with your leach field. If it is a clog that can be removed, otherwise the leach field will need to be relocated.

 

Does a leach field need to be vented?

For most household systems the roof vent will normally provide adequate ventilation for the household plumbing, septic systems and the leach field. For larger septic systems or a commercial building a leach field will probably need to be vented with the leach field vent located on the drain field. This candy cain type pipe can be hidden with a plant or shrub that has very shallow roots and will not enter the perforated pipe.

If the septic tank or leach field is not vented properly this can lead to harmful gases building up in the plumbing and house, some of which are potentially harmful to pets and humans.

 

Can a leach field be repaired?

Depending on the leach field problem, a septic professional will need to diagnose the issue and recommend the correct repair or replacement of the septic field. See septic services quotes for more information.

 

Does every conventional septic system have absorption fields?

Yes, every conventional septic system has a leach field as part of the liquid waste treatment process. Learn more about conventional septic systems.

 

What is a leach line?

A leach line is the final small pipe that deliver the water into the soil for final treatment.

 

Can you build a deck or shed over leach fields?

Leach fields need a combination of good native soil, undisturbed soil, grass and open air to aid in the wastewater treatment, yard drainage and evaporation in order for a drain field to function properly.

A structure like a deck is too heavy to be added over septic system components. Another big problem with a deck or structure like a shed is it stops light that allows grass to grow. Grass stops erosion and exposure of the leach field trenches as well as stopping evaporation of wastewater flows. Depending on local building codes, it is unlikely that a septic system passes inspection if a structure is built on top of the drainage field.

 

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