What Are Leach Lines, and When Should They Be Replaced?

Leach lines, also known as drainage fields or leach fields, are an important component of many septic systems. They help disperse wastewater from the septic tank into the soil, where further treatment occurs. Understanding what leach lines are and when they may need replacing is key for proper septic system function.

What is a Leach Line?

A leach line, or drainage field, is a series of underground pipes laid in gravel filled trenches that allow effluent from the septic tank to percolate into the surrounding soil. The leach field provides further treatment and dispersal of the wastewater.

Specifically, a typical leach line system consists of:

  • Perforated Pipes: These are laid in the trenches and allow effluent distribution. The perforations let the wastewater seep out.
  • Gravel: Surrounding the pipes, gravel aids in dispersing the effluent.
  • Soil: The native soil provides final filtration and treatment as the effluent percolates through it.
  • Trenches: Long, narrow trenches, dug around 12-36 inches wide, hold the leach lines. Trenches are usually 2-3 feet deep and 100-200 feet long.
  • Distribution Box: This regulates wastewater flow into the various leach lines if there are more than one.

The leach field size is designed based on the estimated amount of wastewater generation. The soil type also determines sizing needs. Clay-like soils require a larger leach field than sandy soils that allow faster water movement.

How Do Leach Lines Work?

Leach lines work through a combination of physical, biological, and chemical processes within the soil. Here is an overview:

  • Effluent Dispersal: The perforated pipes and gravel help distribute the wastewater over a large soil area for treatment. Even distribution prevents overloading.
  • Filtration: As the effluent seeps from the pipes into the gravel and surrounding soil, particles are filtered out. Soil acts as an effective filter medium.
  • Adsorption: Soil particles attract and adhere various chemicals and nutrients in the effluent through adsorption. This removes them from the wastewater.
  • Biodegradation: Soil microorganisms, such as bacteria, break down and digest organic matter in the wastewater through biodegradation.
  • Nitrification/Denitrification: Microorganisms convert ammonia in the effluent first to nitrite and then to nitrate via nitrification. Other bacteria convert the nitrate to nitrogen gas that is released to the atmosphere in a process called denitrification.
  • Percolation: Gravity and capillary action help the treated effluent percolate further down through the soil layers.

This natural soil-based treatment process results in much cleaner water dispersing from the leach field compared to the septic tank effluent. It allows environmentally safe dispersal of the wastewater.

Leach Line Materials

Modern leach lines are made from durable, long-lasting synthetics designed for the demanding subsurface wastewater dispersal environment. Here are some common materials:

  • PVC or ABS Plastic: The perforated distribution pipes are typically made from rigid PVC or ABS plastics. They resist corrosion and have a long service life.
  • polyethylene: Flexible corrugated polyethylene pipes are also an option for leach lines. Not as durable as rigid plastic, but can better handle some soil movements.
  • Chamber Systems: These are constructed leach line alternatives made from polyethylene or similar synthetics. Chambers create an open space belowground for effluent dispersal.
  • Gravel: Washed coarse gravel, usually 1/2 to 2 inches size, surrounds traditional pipe leach lines. Gravel should be durable and inert.
  • Geotextile Fabric: This may wrap gravel and pipes to prevent soil intrusion. The permeable fabric keeps the leach field clean.
  • Distribution Box: Typically made from concrete or tough plastic, these split and direct effluent into multiple leach lines.

Quality materials resistant to chemicals and soils are vital for long leach line life. Professional installation per local codes is also key.

Signs Your Leach Lines May Need Replacement

With proper design, quality materials, and maintenance, leach lines can last for decades. However, there are some signs indicating aging leach lines may need replacing:

  • Slow Draining Plumbing Fixtures: Sinks, tubs, etc. draining slowly suggest the leach field cannot accept effluent fast enough. Pipes may be clogged.
  • Gurgling Sounds: Gurgling from plumbing fixtures can mean sewage is backing up due to leach field failure. Air is being forced back up the pipes.
  • Plumbing Backups: Sewage backup is a severe sign of leach field failure. Wastewater has nowhere to go.
  • Surface Ponding: Standing water or soggy soil over the leach field indicates it cannot accept effluent. Pipes are likely clogged.
  • Lush Grass Growth: Excess nutrient loading from leach field effluent may cause unusually green, rapid grass growth above trenches. Can indicate failure.
  • Sewage Odors: Strong wastewater odors around the leach field suggest improper treatment. May be due to excessive loading or clogged soils.
  • Old Age: Leach fields over 30-50 years old are reaching the end of their normal life expectancy. Expect problems.
  • Improper Siting: Poor drainage, high groundwater, or compacted soils can cause premature failures.

These signs indicate it is time to have a professional inspect and test the leach field. Replacement or repairs may be needed.

When Should Leach Lines Be Replaced?

There are several situations that indicate leach lines have failed or are failing and need replacing:

1. Confirmed Failure: If inspection and testing shows the leach field is no longer absorbing all wastewater, it must be replaced. This could be due to age, improper sizing, clogging, etc.

2. Chronic Plumbing Backups: Any occurrence of sewage backups is unacceptable. The leach field needs replacement if it can’t prevent this.

3. Age Over 50 Years: Leach fields older than 50 years are on borrowed time. Strongly consider replacement, even if not yet failed.

4. Lack of Space for New Field: If the current leach field is at capacity and there is no room to install a second one, replacement is required.

5. Record of Past Issues: Consistent previous problems suggest the system cannot provide reliable service. Replacement is the prudent choice.

6. Renovations Increasing Wastewater: Upgrades like new bedrooms that increase wastewater volumes require upsizing or replacing the leach field.

7. Sale of the Property: Many jurisdictions require leach field replacement before property sale after a certain age. Check local regulations.

In summary, replacement is mandated if the leach field demonstrably fails. It is also smart to proactively replace older systems. Real estate transactions often provide impetus.

Leach Field Replacement Process

Replacing a failed or underperforming leach field is a major undertaking, but is necessary for a property to have a code-compliant, environmentally sound septic system. Here is an overview of the typical leach field replacement process:

Site Evaluation: A certified site evaluator conducts deep soil borings, percolation tests, and other analyses to determine the new leach field location and design needs.

Design: An engineer or designer creates the plans for the new leach field based on wastewater loads, soils, site features, and local codes.

Permitting: Construction permits must be obtained from the local health department or jurisdiction before work commences.

Construction: A backhoe or excavator digs out the old leach field piping and gravel. The new trenches are dug, gravel added, and new leach lines installed per the approved design.

Inspection: The local health authority inspects the replacement work before backfilling trenches to ensure proper materials and installation.

Reconnection: Plumbing from the septic tank is re-routed to supply effluent to the new leach field. The old one is taken offline.

As-builts: The designer provides as-built drawings showing the actual replacement components. This is kept for permit records.

Landscaping: Once backfilled and settled, the surface is graded for proper drainage and landscaped to match surroundings.

Replacing a leach field is complex and must meet all construction codes. Involving qualified professionals is strongly advised. Proper installation ensures a long-lasting, problem-free system.

Alternative Leach Field Designs

Traditional leach fields with gravel trenches and perforated plastic pipes have been used for decades. However, some alternative designs are also acceptable in many jurisdictions:

  • Chamber Systems: These are buried plastic chambers with open undersides that replace gravel trenches. Effluent disperses through the chambers into the soil.
  • Sand Lined Trenches: Sand can be used in place of gravel to surround the leach pipes. The sand filters effluent.
  • Pressurized Systems: Small pumps can distribute effluent through pressurized pipes in more shallow, narrow trenches.
  • Mound Systems: A mounded sand bed over the field allows installation in sites with high water tables. Effluent percolates down through the mound.
  • Drip Dispersal: Much like a drip irrigation system, small drip emitters can release effluent into soils. Used for sites with very tight soils.
  • Packed Bed Media: Proprietary media like tires chips or foam peanuts fill the trenches instead of gravel to disperse effluent.

Alternative leach fields can be appropriate for sites with difficult soils or other constraints. An experienced designer selects the right technology.

Cost To Replace Leach Field

Replacing an entire leach field is a major undertaking and has significant costs. Here are typical price ranges:

  • Basic System: $5,000 – $15,000
  • Complex Installation: $15,000 – $30,000
  • Alternative System: $15,000 – $50,000

Many factors affect the total project cost:

  • Permit Fees: These vary by county but can be $500 – $2,000.
  • Site Work: Difficult access or extensive vegetation removal increases costs.
  • Soil Issues: Poor soils requiring sand, chambers, or other alternatives are more expensive.
  • Size: More trenches, piping, gravel and other components raise costs for larger systems.
  • System Type: Alternative pressurized, mound, sand filter, or proprietary systems cost much more than basic gravity systems.
  • Landscaping: Extensive restoration or plantings after installation add cost.
  • Designer Fees: Engineering design services can range from $1,000 – $5,000 or more.

Proper leach field replacement often costs $10,000 to $20,000+, so homeowners must plan and budget accordingly. This maintenance ensures a code-compliant, environmentally sound septic system.

DIY Leach Field Replacement

Some homeowners consider do-it-yourself leach field replacement to save on the high costs. This is NOT recommended for these key reasons:

No Permitting: As an unlicensed installer, the homeowner usually cannot obtain required construction permits from the health department. Installing a system without permits risks substantial fines.

Improper Materials: Homeowners may unknowingly obtain incorrect materials that do not meet local regulations. This can lead to early failures.

Inadequate Design: Sizing and locating the new system requires specialized expertise. Incorrect design can cause illegal and dangerous failures.

Safety Issues: Installation risks trench collapses, heavy equipment hazards, and other dangers. Lack of training heightens risks.

No Oversight: Without permitted installation, there is no health department inspection of construction. Defects may go unnoticed.

No Recourse: DIY replacement without permits means no contractor guarantees or bonding. There is no accountability for problems.

Resale Issues: Replacement by a licensed contractor facilitates property sales. DIY work can prevent sales or require costly re-installation.

Leave leach field replacement to experienced, licensed septic contractors. DIY risks illegal, unsafe, underperforming systems that become costly headaches. Hire the pros and do it right the first time.

FAQs About Leach Line Replacement

Here are answers to some frequently asked questions homeowners have about replacing their septic system leach field:

What is the cost to replace a leach field?

The typical range is $10,000 – $20,000, but costs vary widely based on site conditions, system size and type, permit fees, and other factors. Complex installations with engineering can cost $30,000+.

How long does leach field replacement take?

Most full leach field replacements take 2-5 days from start to finish. Permitting, site work, and inspections can lengthen the overall timeline.

Can I replace leach field myself?

This is not advisable, as proper permitting, expertise, and equipment is needed. Hire a licensed septic contractor for code-compliant, safe replacement.

Does a leach field need replacing if it smells?

A sewage odor from the leach field area indicates the system is overloaded or has failed. Yes, replacement is likely needed in this situation.

What happens if leach field is not replaced?

An unrepaired failed leach field will overflow untreated sewage onto ground surfaces and into waterways. This is an environmental and health hazard requiring urgent replacement.

How often should a leach field be replaced?

With proper maintenance, a well-designed leach field can last 20-50 years. More complex alternative systems may need replacement sooner.

Can a leach field be repaired instead of replaced?

Partial repairs are possible in some cases, by replacing piping or removing blockages. However, once a leach field has truly failed, full replacement is usually required.

Should leach fields be replaced when selling a house?

If over 30 years old, leach field replacement is smart when selling. Even if working, an older system can deter buyers or require replacement by them soon after purchase.


Leach fields, also called drain fields or leach beds, provide essential wastewater dispersal and treatment in many septic systems. The perforated pipes and gravel trenches dispense septic tank effluent into underlying soils. A properly functioning leach field prevents pollution. However, these components do age and eventually need replacement. Signs of failure include backups, odors, and soggy ground. Replacement costs vary based on system size and type but expect $10,000 to $20,000 or more. DIY installation is NOT recommended. Instead, work with qualified professionals to ensure your new leach field meets all codes and provides decades of reliable service. Proactive replacement can help avoid emergency failures and enhance property value and marketability.