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Most people have a general idea of what a septic tank does. What they may not understand is what the leach field does and the importance of this major component of the septic system.

Basic septic systems have two main parts: a septic tank and an absorption field. A septic tank is a buried, water-tight container usually made of concrete, fiberglass, or polyethylene. The breakdown of sewage begins in the tank.

First, wastewater from the household flows into the tank through a drainage pipe. Then the tank holds the wastewater from the household long enough for the solids to settle to the bottom of the tank. During this process, oil and grease in the water float to the top and form a scum on the surface. Finally, the liquid part of the wastewater (effluent) exits the tank and drains into the absorption field.

The second part of the system is the leach field. The leach field is a shallow, covered, excavation made in unsaturated soil. This soil absorbs and percolates the wastewater, allowing harmful substances to be broken down naturally.

Here, we would like to detail what the leach field is, what it does and answer some commonly asked questions so you are educated on the subject should you ever need the information.

What is a Leach Field?

Also known as a drain field or absorption field, the leach field is a portion of area that is attached to a septic tank for an individual home and makes up the final processing step or sewage treatment in a septic system. The leach field is a network of underground pipes containing many small holes that works as a disposal filter for contaminants and liquids after they have been anaerobically digested and pass through the septic tank. The leach field will typically contain a system of trenches and gravel (or another porous material) covered in soil.

The main purpose of the leach field is to disperse liquids from the septic tank in the an area of soil by means of drains which eventually gets spread out in the large area known as the leach field. When the liquid waste passes through the leach field that is made up of earth, gravel and other similar material, it gets all the organic matter removed and transformed into useful substances.

A properly designed leach field considers hydraulics so the material can properly move through it, and catabolism for the biochemical oxygen demands of the wastewater.

What Is the Best Leach Field Distance From Your House?

The leach field is usually placed in an open, flat area close to the house. The actual distance may vary according to the property’s layout and the systems’ specifics. It is best to make the decision with the help of a West Coast Sanitation specialist.

The goal is to have the leach field close enough to the house that you can avoid unnecessary piping expenses but far enough to prevent water infiltration into the house’s walls. Other factors for placement include such things as soil composition, tree roots, sloping requirements, etc.

The bottom line is that it takes more than knowing the leach field definition and consulting a leach field size chart to get a functioning system. It takes even more to know how to fix leach field problems.

Some questions you can ask your septic installation professional:

  • Can you have a septic tank without a leach field?
  • How does a septic tank and leach field work?
  • How deep is a leach field typically installed?
  • What are the minimum leach field maintenance requirements?
  • How long should a leach field last?

Signs a Drain Field is Failing

There are a number of ways a septic field can fail. 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 the sludge is not pumped out of the tank, it can breech the filter and seep into the lines of the septic leach field. Eventually, the opening and the lines will become so backed up that effluent cannot exit the tank properly and it will back up into the building.

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

  • Gurgling pipes
  • 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

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
  • Ensure you know when your next septic tank pump is due
  • Do not put harmful chemicals (such as bleach or ammonia based cleaners) down the sink or toilet
  • Only flush human waste and approved toilet paper down the toilet
  • Avoid using a garbage disposal, if you do use it infrequently
  • Do not do multiple 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
  • Never put motor oil, paint or grease down the household plumbing

Drain Field Size, Layout and Leach Field Design

The size necessary for your drain field will depend on a few factors. The soil should be tested for a percolation rate first. You can run the percolation test on your own, or hire someone to do this.

The size of the field will be based on the size of the home and the rate of percolation. A typical home with a good percolation rate may require as little as 4,500 square feet of field or as much as 9,000 square feet with a poor percolation rate.

Another consideration should be local zoning regulations. Most localities have ordinances determining how far the field needs to be from property lines, streams, wells, water supplies, or any protected land.

A proper drain field needs to have perforated pipes buried in gravel trenches throughout the field. The trenches should have a slight slope, usually less than 1/8th inch per foot. The pipes will need to be placed in gravel and covered with more gravel. When you map out the piping, be sure to create a sketch that reflects the depth of the field accurately. This will allow you to plan for the amount of soil under the gravel, the amount of gravel, the space needed for the pipe, and the amount of gravel needed for the cover. A drain field trench will usually need to be about 30 inches deep.

The shape or footprint, of a septic system drainfield or leaching bed is determined by the following considerations:

  • The size and shape of the land available in which septic components can be placed.
  • The slope of the land in the area where septic components will be placed.
  • The soil characteristics (for example the soil percolation rate – the rate at which the soil can absorb septic effluent)
  • The anticipated average and maximum daily wastewater flow
  • The type of septic system since different effluent handling methods need different total effluent disposal areas and different total linear feet
  • The exact locations of property boundaries, and the locations of any nearby wells, streams, lakes, driveways, buildings, or any other site features that require a separation distance between septic system components and that site feature.
  • The local building codes which may specify certain septic component distances, set-backs, capacities, as well as the requirement for a reserve area on the site to permit future septic system expansion, repair, or replacement.
  • Local obstructions such as trees, boulders, etc.


Call West Coast Sanitation Today!

When the appointment is set for the septic inspector to come out, make time to be there and watch how things proceed. This commitment to the sale is important. Everyone involved wants a fast sale and this is one you do not want to shortcut to come at your expense.

At West Coast Sanitation, we understand the value and importance of a septic system inspection prior to buying or selling a home. Our professional inspectors strive to exceed your expectations and help you obtain the essential information you need to make an informed decision.

Call us at (951) 780-5922 right away. We have professionals ready to answer your questions.