10 reasons why leach fields and drainage fields fail | howtosquirrel.com (2023)

I have owned a house with a lye field for over 34 years. In my work I have carried out repairs and replaced lye fields. I'd like to share what I've learned from doing some research and what I've experienced with why a leach field might fail.

Why does a leach field or a drainage field fail.A seepage or runoff field receives the treated water from a septic tank and disperses the water into the air through absorption in the soil and evaporation with the help of a cover crop such as grass. A leach field or drainage field fails when the amount of water entering the field exceeds the amount of water that can be evaporated or absorbed.*A lye field and a drainage field are the same*

The simplified reasons leading to leach field failure are:
The bottom is clogged with solids from the tank and will not absorb water
The pipes that supply the field are clogged and the water cannot reach the entire field
The evaporation process was interrupted by compaction or coverage
More water is injected into the field than intended

Below are ten reasons why a leach field or drainage field fails

1. Lack of maintenance of the septic tank.
Septic tanks need to be pumped every 3-5 years to remove the solids accumulated from their use. The way a septic tank works is that the waste from your toilets, sinks, showers and laundry goes into the tank and bacteria breaks down the organic solids into sludge that settles at the bottom of the tank. Non-organic material such as plastics, grease, hair and soap accumulate in the floating foam layer. If the mud or floating scum enters the line feeding the leach field, your leach field will fail. The easy way to prevent this is to pump the tank and don't flush anything that isn't human waste or toilet paper.

Visit our article onHow to maintain a septic tank and add a riser

2. Excessive water consumption.
A leach field is designed to handle a certain amount of water entering the system per day. A leach field is designed such that the designing architect or engineer directs a perc test to be performed on the area where the leach field is to be placed. What a perc test does is find out how much water the soil type absorbs in a given amount of time. This will determine the size and type of leach field required for your home. A 1 bedroom house has a lower occupancy and uses less water and requires a smaller suds field than a 3 bedroom house in the same location.
To find out what it's all about and how to do a perc test, read our article on

"How to do a Perc Test" (coming soon)

List of things your leach field is not designed for

  • leaking faucets
  • Toilets that won't stop running
  • Sudden toilet use by an additional guest (weekend party or wedding reception)
  • Sudden increase in consecutive laundry loads
  • Adding a sump pump or gutters to the system
  • Draining a hot tub or pool into the system

Leaching field failure may only be temporary if the toilet or faucet is leaking. The saturated field will return to normal after you stop the leak.

(Video) Failed Leach field

Check out our articleWhy is my toilet running and how can I stop it?

The failure of the leach field becomes permanent when the sudden flow of water into the septic tank stirs up the sludge on the ground and the particles flow into the leach field and prevent the ground from absorbing the water by forming a film or what I call black slime in the field the floor. When this black slime is formed, you need to replace the box.

3. Trees or landscape shrubs planted on or near the field

Trees or shrubs should never be planted on or near the leach field. I know it looks tempting, lots of moisture and a wide open stain, but don't do it. The nature of the tree or shrub is there for its roots to travel and find moisture. You will of course also hike and enter the lye pipelines. The pipes have holes that run along the bottom and that is where the water will flow to get into the lye field and this is where the roots will enter. The roots will completely stop the flow of water over time and the leaching field will need to be replaced. I've seen this many times. The best trees to plant in your lye field are not trees.

4. Drive cars or heavy equipment across the leach field

Driving over a leach field damages the field by:

  • soil compaction

If the soil of the leach field is compacted by heavy tire traffic, the absorption rate will be negatively affected. When soil becomes compacted, there is no easy way to fix it other than removing the affected soil and replacing it with new soil.

  • Damage the pipes by crushing or breaking them

If the tires drive over the soakaway lines, especially if the ground is wet, there is a good chance the pipes will be crushed or displaced and the connections severed. The pipe connections are not glued in a lye field. If the tube is crushed or a connection loosens, that tube will stop working and cause a field outage. The crushed or severed pipe can be repaired by digging up the affected area and repairing the crushed or severed area.

  • Forcing earth into the rock reserve layer

The way a lateral pipeline for a leach field is constructed is to dig a trench about 20 to 24 inches wide and to the depth required by the design. 6 inches of 2 inch washed stone is placed in the trench, then the pipeline with the holes on the bottom and more stone until you get a 6 inch cover over the pipe.

The stone offers empty spaces between them that serve as a reservoir for the water until the ground absorbs it.

(Video) LEACH Fields: 8 Things You Should Know

A filter is then placed over the stone before earth is laid over it. Cloth or straw is used to hold back the soil. If you drive across the field when it is wet you can damage this filter and cause the top soil to seep into the rock that fills the reservoir. The only solution to this is to replace the leach field.

5. Construction of a parking lot on the leach field

Building a parking lot on the leach field damages it by:

  • compaction of the soil
  • Prevents the water from evaporating

The second way the leach field removes the water you put into it is through evaporation. Covering the field with material for parking reduces or stops the evaporation process that leads to field failure. Removing all the material involved and replacing it with new permeable material is the solution. This is very expensive.

6. Raising the ground level over the leach field with fill soil

Leach fields are designed to operate at a specific depth. Bringing in padding and raising the ground level will accomplish two things

  • Compact the soil
  • Stop evaporation

Your field may work for a short time, but if it cannot be repaired you will need to build a new field at the new height and possibly install a lifting station to bring the water to the new field.

7. Change of water drainage level

The drainage level is the way the rainwater flows over the ground. You have seen water standing in a low spot in a yard or field after a heavy rain. The same could happen to your leach field and it would be bad for your leach field.
If you have done landscaping work, it should not run off into the leach field. The same goes for your gutter downspouts. They should not drain into your leach field.

The water from a rain should always run away from your leachate field in order for it to work efficiently.

(Video) Restoring A Septic Drain Field: First Steps (Least Vs. Most Expensive)

8. Constructing a storage shed, pool or patio on the leach field

Building one of these has the same effect as building a parking lot on the Leach Field.
soil compaction
evaporation reduction
The system may never fail completely, but the system will not function as intended once built. Best not to build on it.

9. Junction box failure

The junction box connects to the pipe that comes out of your septic tank and directs water to each of your scour field lines. The leach field has multiple lines. The type of floor and the number of bedrooms determine the number of lines laid out in it.

The junction box can be made of cement, plastic or steel. Steel are not common. The most common are plastic and cement.

Junction boxes usually fail when something heavy drives over them and crushes the box. You might not realize it's broken. If it breaks, it could fill with soil and stop the distribution of water to the leach field lines. This is an easy fix by replacing the broken box with a new one.

10. Failure of the septic tank, exit pipe falls off

A septic tank is designed so that the sewage and solids enter the tank and are routed down through an elbow or a tee that acts as an elbow into the middle portion of the tank (roughly 12 inches).

The tee is a lot smarter as it can be cleaned if it gets clogged with grease or soap.

The exit pipe is the same setup, except the area it draws from is a few inches lower than the tee that feeds the tank. This configuration reduces the likelihood of raw sewage entering the leach field and causing a failure.

(Video) Your Septic System: Worst Mistakes

The exit tube is glued and the problem occurs when the glue fails and causes the bow or bottom tube to fall off. Then raw sewage will flow into the field and the black slime will start to grow and you will get a lye field outage. I fixed fields that this happened.
The bad news is there isn't much you can do to prevent this from happening.

The good news is that it doesn't happen that often.

I hope this article helped answer your question, here's a bonus that fits in with this article.
How long does a leach field or drainage field last
This is a question that has no set answer. A drainage or leach field should last between 30 and 50+ years. It depends on the soil type whether the septic tank has been properly maintained and whether the field has been properly designed and installed.

I built my house in 1984 and the leach field is still working as designed. My parents' house has been on the Laugenfeld for 50 years and it hasn't had any problems. I've seen leach fields last over 50 years and seen them fail in 10 years. I would like to give you a better answer, I can only give you the truth as I know it. It depends on your floor type, how it was designed and maintained, and whether any of the above conditions have occurred.

Best wishes
Gary 11.10.2018


Oregon State University

Washington State Department of Health and Human Services

University of Nevada

Environmental Protection Agency

(Video) how to fix your septic tank drain field


What can cause leach field to fail? ›

Most leaching fields fail due to biological or hydraulic overload. Hydraulic overload occurs when too much water is sent to the septic tank. For this reason, it is recommended that tasks such as laundry be spread out during the week instead of doing too much at once. This prevents hydraulic overload of the system.

Why do drain fields go bad? ›

Oversaturation. Dripping faucets, running commodes, and malfunctioning water softeners put extra water into the septic system, which can flood out your drainfield. Higher-than-normal usage on the system from occupants or visitors can overload the system as well.

Why is my leach field not draining? ›

Note: when a septic system that's less than 20 years old fails to drain, it's sometimes a sign of tree roots clogging the lines, issues with the surrounding soil, structural damage to a pipe, or a faulty design. You can use a sewer jetter to clean perforated PVC septic leach field lines from 2" to 6" ID.

What clogs a leach field? ›

Pump it Regularly – Clogs in the leach line typically occur because sludge or FOG make their way from the septic tank into the outlet pipe. When you notice sludge is within 12 inches of the outlet pipe, or FOG within 3 inches, it's time to have your tank pumped.

Does heavy rain affect leach field? ›

Heavy rains and flooding can cause major problems with septic systems. If this happens, affected residents not served by central wastewater systems may need to take precautions to prevent possible sewage contamination. Human exposure to wastewater can lead to disease transmission.

What is the most common reason drains fail? ›

The problem of blocked drains occurs when foreign materials such as soap, hair, food, and fats build up between the drain-pipe and other pipes that flow at the bottom. In the beginning, the materials are in a small amount. With time, as the amount of objects increases, it stops water to flow freely.

How often do drain fields fail? ›

It's important to consider the life expectancy of a drain-field, too. Under normal conditions and good care, a leach-field will last for 50 years or more.

How often do septic drain fields fail? ›

How long does a septic system drain field last? A well-built and properly maintained drainfield should last for at least 20 years.

What are the signs of failing drainfield? ›

4 Signs of Leach Field Failure
  • Ground Saturation or Puddles. The purpose of a leach field (or sometimes called a drain field) is just that – wastewater should absorb into the soil and get broken down by bacteria. ...
  • Slow Drainage or Backup. ...
  • Excessive Grass Growth. ...
  • Smelly Odors.
Oct 26, 2021

Can heavy rain cause septic backup? ›

It is common to have a septic back up after or even during a heavy rain. Significant rainfall can quickly flood the ground around the soil absorption area (drainfield) leaving it saturated, making it impossible for water to flow out of your septic system.

How long does it take for a leach field to recover? ›

The rejuvenation process takes about two years. During this time, naturally occurring organisms decompose the clogging mat that has formed and return the absorptive system to near original capacity.

How do you damage a leach field? ›

You can physically damage your drain-field by driving over it or allowing livestock to compress the soil and damage the pipes in the ground. If your pipes are damaged and the soil overly compressed, the effluent cannot properly flow through the soil, resulting in puddles and a failed drain-field.

How do you keep a leach field healthy? ›

  1. Regularly inspect and maintain your septic system. ...
  2. Pump your septic tank as needed. ...
  3. Keep your septic tank lids closed and secured. ...
  4. Be water-wise. ...
  5. Direct water from land and roof drains away from the drainfield. ...
  6. Landscape with love. ...
  7. Keep septic tank lids easily accessible.
Apr 3, 2022

Can you replace a leach field in the same spot? ›

This is usually possible from an engineering standpoint, but messy and expensive. Basically, you need to excavate and remove the entire drain field, plus some of the surrounding soil. This needs to be hauled away and disposed of as hazardous waste, and then replaced with properly engineered and compacted fill.

Can a leach field get clogged? ›

Over time, the leach field can become damaged or clogged due to buildup of material. A full septic tank can cause problems by allowing solid waste and sludge to overflow into the drain field. While a clogged drain field cannot be snaked out and cleared like a drain pipe, you can take steps to alleviate the problem.

How long does it take for a leach field to dry out after rain? ›

The groundwater will take time to recede to the level of the bottom of the drainfield. This could happen within a week or two or require a couple of months.

How many years should a septic system last? ›

Septic systems can last up to 25 years — or indefinitely in rare cases. It completely depends on the maintenance of the system. If you get regular inspections and make repairs as needed, your concrete septic tank can last longer than a lifetime.

What are four effects of poor drainage system? ›

Building material deterioration. Erosion. Insect and rodent infestations–spiders, reptiles etc. Mold growth and wood rot.

What are three effects of poor drainage system? ›

Issues concerning drainage other than health

Floods can make it impossible for people to move around. Poor drainage can cause landslides and mudflows, which may be a risk to people and their property. Stormwater can erode fertile soil, reducing production.

What are indicators of poor drainage? ›

Signs of poor drainage

Surface water, ponding and flooding. Yellow leaves on plants caused by a lack of nitrogen and oxygen. Machinery tracks. The soil particles pack together into clods.

How long can a failing leach field last? ›

It may last for 50 years or longer. A leach field could outlast multiple owners of a house or property. Events such as natural disasters and catastrophic weather can suddenly damage leach fields.

How much does it cost to unclog a drain field? ›

Drain field repairs vary drastically, as it all comes down to where the problem is located and the ease of access to repair the problem. With these considerations in mind, drain field repairs can cost anywhere from $2,000 to $15,000.

Can a drain field collapse? ›

The drain field is a system of perforated pipes in the ground that are in trenches and surrounded by soil. The drain field is the key part of your sewage system that can cause the entire operation to collapse and cost homeowners thousands of dollars to repair or replace.

How often should a septic field be cleaned? ›

The average household septic system should be inspected at least every three years by a septic service professional. Household septic tanks are typically pumped every three to five years.

Is a septic tank full of water when it rains? ›

Yes! Heavy rain and other water sources that oversaturate the soil around your septic tank can cause your tank to flood. This can be a serious and delicate issue, so be sure to contact a septic tank professional when your system is flooded.

How much water can a leach field handle? ›

How Many People Can A Septic Tank Handle? It comes down to daily water usage. Most residential tanks have a capacity ranging from 750 gallons to 1,250 gallons and the average person uses 60 gallons to 70 gallons of water a day.

How deep is the gravel in a leach field? ›

Granite gravel is the best option for a leach field bed. The gravel amount depends on soil composition and septic system size. Leach field depth should be around 3 to 4 feet, depending on the size of your space.

What happens when leach field is full? ›

If the drainfield is overloaded with too much liquid, it can flood, causing sewage to flow to the ground surface or create backups in toilets and sinks. Finally, the wastewater percolates into the soil, naturally removing harmful coliform bacteria, viruses and nutrients.

What does a healthy leach field look like? ›

One of the apparent signs of a healthy leach field is level and stable soil near the drainfield. When your home's drainfield cannot expel all of the wastewater from the septic tank, it will eventually collect into the ground. This will cause your soil to be “squishy” and even condense on itself.

What are the signs of a failing leach field? ›

Gurgling sounds in the plumbing system. Standing water or damp spots near the septic tank or drainfield. Bad odors around the septic tank or drainfield. Bright green, spongy lush grass over the septic tank or drainfield, even during dry weather.

What is the life expectancy of a leach field? ›

It's important to consider the life expectancy of a drain-field, too. Under normal conditions and good care, a leach-field will last for 50 years or more.

What is the most common cause of septic system failure? ›

Most septic systems malfunction because of inappropriate design or poor maintenance. Some soil-based systems (those with a drain field) are installed at sites with inadequate or inappropriate soils, excessive slopes, or high ground water tables.

Why is my septic tank drain field not working? ›

If the buildup of organic material is not filtered by the septic tank, this can cause the drain-field to fail. If your first step of treatment is not done properly in the septic tank, causing low quality effluent to be discharged to the soil, the build up of organic waste can lead to drain-field failure.

How often should a septic field be pumped? ›

Don't wait until you have a problem. For a typical household, septic tanks are usually pumped every three to five years. Routine pumping can prevent expensive failures such as a clogged drainfield or sewage backing up into the home.

Can you add soil on top of leach field? ›

Never add additional soil over the drain field unless it is a minimal amount used to restore an area that may have been eroded or pulled up by removing another plant. Try not to be overly zealous when tilling the soil for planting. Remember that the drain lines may be as close as 6 inches from the soil surface.

How often should you switch leach fields? ›

Many septic systems have 2 fields that should be switched every 6 – 12 months. If your system was designed with 2 fields, there is most likely a distribution box with 3 pipes. One pipe is from the septic tank or aerator and the other 2 pipes lead to each field.

Can you reuse an old leach field? ›

Use the tank to treat and store graywater for indoor, non-potable uses, and reuse the leach field to infiltrate stormwater.


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