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Glossary

Leach Field

Leach Field

A leach field is a network of underground pipes with small holes in them. It takes the liquid wastewater from your septic tank and slowly lets it soak safely into the soil. You must keep heavy vehicles off this area so you do not crush the pipes.

Reviewed by Jill AshUpdated July 15, 20263 min read

Origin

The word leach comes from the Old English word leccan which means to water or moisten. Builders started using the term for waste systems in the early 1900s to describe how liquid filters through dirt.

How you'll see it used

  • The home inspector noted that the leach field is located in the backyard and advised us not to build our new deck over it.
  • The septic company quoted us 6,500 dollars to install a new leach field because the old pipes were completely clogged with tree roots.
  • I told the landscaper to keep his heavy riding mower off the side yard so he does not crush the leach field pipes.

What a Leach Field Is

The word leach comes from an old English word that means to water or moisten. Builders started using the term in the early 1900s to describe how liquid waste filters through dirt. Today, a leach field is a network of underground pipes with small holes in them. It is the final stop for wastewater in a home with a septic system. Instead of sending waste to a city sewer line, your home treats its own water. The leach field takes the liquid from your septic tank and slowly lets it soak safely into the soil. A leach field usually looks like a large, flat, grassy area in your yard. The size of the field depends on how many bedrooms your house has and how well your soil absorbs water. Sand absorbs liquid quickly, while heavy clay takes much longer.

How It Works

When you flush a toilet or drain a sink, the water travels through your Plumbing into a large underground septic tank. Solid waste settles at the bottom of the tank. The remaining liquid flows out into the leach field pipes. These pipes sit in shallow trenches filled with gravel and covered by dirt and grass. The trenches are usually 1 to 3 feet wide and up to a hundred feet long. A layer of special fabric covers the gravel to stop dirt from falling in and clogging the spaces. As the liquid slowly drips into the trench, the soil acts as a giant natural filter. This process removes harmful viruses and bacteria before the water reaches the groundwater deep below your yard.

Why It Matters to You

A healthy leach field keeps your property safe and clean. If the pipes clog or the soil floods, the liquid has nowhere to go. This can cause raw sewage to back up into your home. It can also cause foul water to pool in your yard. You might notice these warning signs if you check our guide on Smells & Odors around the house. If you see patches of grass that are suddenly much greener and taller than the rest of your lawn, you might have a leak. You might also hear gurgling sounds when you flush your toilets. A failing system is a major health hazard and can ruin your lawn.

What It Costs to Fix or Replace

Replacing a leach field is a huge expense. If your system fails, you will likely need to dig up the old pipes and install new ones in a different part of your yard. A new leach field usually costs 3,000 to 15,000 dollars. Prices depend on the size of your home and the type of soil you have, so keep in mind that ranges vary by location. Minor repairs like fixing a crushed pipe might cost 500 to 1,500 dollars. Before a contractor can build or replace a leach field, they must do a percolation test. This test measures how fast water drains into your dirt. You will also need special permits from your local health department.

How to Protect Your System

You must treat the area above your leach field with care. The pipes sit just a few feet below the surface.

  • Don't drive cars or heavy trucks over the grass. The weight will easily crush the plastic pipes.
  • Don't plant trees or large shrubs near the field. Roots will grow into the pipes and block the water.
  • Don't build sheds, patios, or pools on top of the area.
  • Route your roof gutters and sump pump drains away from the field. Extra rainwater will flood the soil and stop it from absorbing waste.

If you need help moving rainwater away, look into Landscaping, Drainage & Outdoor solutions.

Never flush harsh chemicals, grease, or flushable wipes down your toilets. These items destroy the good bacteria in your tank and cause your leach field to fail very quickly.

Frequently asked

Can I plant a vegetable garden over my leach field?

You should never plant a vegetable garden over your leach field. The plants could absorb harmful bacteria from the wastewater below the soil. It is best to stick to shallow grass to keep the area safe and functional.

How long does a leach field last?

A well maintained leach field usually lasts 15 to 25 years. You can extend its life by pumping your septic tank regularly and keeping heavy equipment off the grass.

Why is the grass over my leach field suddenly so green?

Unusually green or tall grass over your leach field is a sign that wastewater is rising to the surface instead of sinking into the soil. This usually means the pipes are clogged or the field is failing. You should call a septic professional to inspect it right away.

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