What is a leach field?

A leach field finishes the job the septic tank starts. The tank separates solids from liquid. The leach field then sends that liquid into the ground, where the soil treats it.

What's the difference between a leach field and a drain field?

There isn't one. Leach field, drain field, drainfield, leach lines, absorption field and soil treatment area all name the same part of the system. Which one you see mostly depends on the region or the document.

How does a leach field work?

1. Liquid, called effluent, leaves the septic tank through an outlet.
2. On many systems, a distribution box divides the flow between lines.
3. Perforated pipes or plastic chambers release the liquid along shallow trenches.
4. The liquid soaks into unsaturated soil.
5. As it moves down, the soil and its microbes remove harmful bacteria, viruses and nutrients before the water reaches groundwater.

That last step needs air spaces in the soil. When soil stays saturated, the field can't accept or treat water properly.

What does a leach field look like?

From the surface, a healthy field usually looks like ordinary lawn. Underneath, a conventional field is a set of trenches, each holding gravel or chambers with fabric and soil on top.

How big is it? Ohio State University Extension says a three-bedroom home's system can be up to 138 feet long, depending on soil and site, usually split into sections. Sizes vary a lot, though, and your permit record is the only reliable guide to yours.

Types of leach field

Type	How it spreads water	Where it's used
Gravel trench	Perforated pipe in a stone-filled trench	Sites with enough suitable soil and space
Chamber	Connected plastic chambers with no gravel	High water tables, variable flows, areas short of gravel
Drip	Small tubing in the top 6 to 12 inches of soil	Many field types, but needs a dose tank and power
Mound	A trench inside a built-up sand mound	Shallow soil, high groundwater or shallow bedrock

How long does a leach field last?

There's no fixed lifespan. What the EPA does say is that a biomat, the slimy layer that forms in the field, can thicken once a field is more than 25 to 30 years old and cut how much water it can discharge. At that age, the EPA advises owners to start planning an upgrade before it turns into an emergency.

What damages a leach field?

NC State Extension names these common causes of failure:

• Too much water. Leaks, extra appliances and sump pumps can overload the system.
• Runoff. Water from roofs, roads or paving can saturate the soil.
• Skipped pumping. Solids that escape the tank clog the soil pores.
• Physical damage. Driving or building over the field can crush pipes and compact soil.
• Roots. Tree roots can clog the lines.

How do you protect one?

Most of it is about keeping weight and extra water off the field:

• Keep cars and heavy equipment off it.
• Send roof drains and sump pumps away from it.
• Plant trees at a safe distance. A septic professional can advise on yours.
• Check with your permitting authority before building anything on it.
• Keep the tank pumped on schedule.

Quick answers

Is a leach field the same as a septic tank?

No. The tank separates solids from liquid, and the leach field releases that liquid into the soil.

Can you park on a leach field?

No. The EPA says not to park or drive on one, because vehicles can damage the system.