Leach fields, also known as septic tank drain fields, or simply septic tank drains, are an undervalued part of every rural residential septic system.

Homeowners who rely on a septic tank may not understand how leach field design and maintenance impact their property’s plumbing and overall value. We’ve got answers to some of the most common questions our plumbers hear about leach field failure – let’s get into it!

First, What Is a Leach Field?

Leach fields are meticulously designed systems of perforated pipes underground that surround the septic tank and safely disperse wastewater. As bacteria break down waste material, it gradually drains into the soil through the pipes. The soil naturally filters much of the remaining contaminants as the wastewater seeps deeper underground.

How Deep Is a Septic Drain Field Buried?

Leach field lines are buried three to four feet below the surface during installation. The drain field system is surprisingly large, usually nearly 100 feet long, and each pipe is buried five to six feet apart. The leach field piping is connected to the septic tank, typically on a wide, flat area of the property.

The lines are also buried in a mix of gravel and soil aggregate to promote filtration and to mitigate the pipes' shifting or settling in softer soils.

How Do I Find My Septic Tank Drain Field?

You may already have a map of your septic tank on hand! Most states require a septic system map to be included after construction and whenever the property is purchased.

While most residential septic tank drain field layouts are relatively similar, it’s important for homeowners to find every septic system component with pinpoint accuracy in the event of leach field failure or other septic tank issues.

What Are the Most Common Leach Field Problems?

In-home drain speed is often the most noticeable issue caused by a poorly designed leach field or one in dire need of maintenance. There are a few tell-tale signs that your septic system, including your drain field, requires closer inspection.

Slow drains. While most slow-draining plumbing issues are caused by a blockage inside the home, clogged leach lines can also cause backups in the sink, shower, or toilet. In most cases, a sluggish septic tank field is caused by an imperfect design, low bacteria count in the tank itself, or blockages in the pipes.
Tree roots. Tree roots are the bane of many exterior plumbing components, and drain fields aren’t immune. Over time, tree roots can clog the small perforations that allow wastewater to exit the pipes.
Outdoor issues. There are a few reliable outdoor signs of drain field problems, too. If you notice a patch of especially green or fast-growing grass, soft ground, or standing water, there’s a good chance your leach field is to blame. The cause may vary, but these issues are usually the result of poor drainage, blocked pipes, or leaks at any part of the septic system.

Not entirely sure what the issue might be? Get to the bottom of these and other septic and sewer problems with a call to your local Benjamin Franklin Plumbing.

How Long Does a Leach Field Last?

A well-designed leach field will last between 15 and 50 years. The dramatic lifespan difference is based on several factors, including:

Maintenance – Regular inspections and pumping every 5-10 years can extend the field’s functional life.
Soil conditions – Well-draining soil like sand reduces the risk of backups and clogs. Clay and loam may trap water near pipes, causing rust or blockages.
Water usage – The average volume of water you use at home impacts the field’s lifespan. The more water you use, the more often you’ll need to inspect and potentially repair your drain field.

Can You Have a Septic Tank Without a Leach Field?

No, because a septic tank is only one part of the system. Before water goes to the drain field, septic tanks collect and separate solid and liquid waste, providing a safe space for bacteria to begin breaking down wastewater. A functioning leach field is a legal requirement in most parts of the country and typically requires a permit from the local health department.

Can You Replace a Leach Field in the Same Spot?

Depending on where you live, some local ordinances allow homeowners to replace an existing leach field in the exact same spot, but there are conditions. This usually requires the excavation and removal of contaminated soil before the new installation, which is costly and invasive. In most cases, installing your new leach field in a different location is less expensive. It may mitigate the issues that damaged your old system, such as soil composition or proximity to tree roots.

What Can You Put on Top of a Septic Field?

Out of sight, out of mind doesn’t mean out of trouble. Since septic tank drain field pipes are just a few feet below ground, they’re vulnerable to things happening above ground. Don’t build heavy sheds, decks, or patios above the leach field, and avoid driving stakes or poles into the ground near leach lines. Avoid planting trees, shrubs, or other deep-rooted plants within ten feet of the lines to prevent damage from invasive root structures.

Leach Field FAQs – Your Questions, Answered!