I have owned a house with a leach field for over 34 years. In my line of work I have done repairs and replaced leach fields. I would like to share what I have learned with some research and what I have experienced with why a leach field might fail.
Why does a leach field or drain field fail. A leach field or drain field accepts the processed water from a septic tank and disperses the water by absorption into the soil and evaporation into the air with the help of a cover plant like grass . A leach field or drain field will fail when the amount of water that enters the field exceeds the amount of water that can be evaporated or absorbed. *A leach field and a drain field is the same thing*
The simplified reasons that cause a leach field failure are
the soil has become clogged with solids from the tank and will not absorb water
the lines supplying the field get clogged and water can not get to the entire field
The evaporation process has been interrupted by compaction or cover
More water is being injected into the field than it was designed for
Listed below are ten reasons why a leach field or drain field will fail
1.Lack of septic tank maintenance.
Septic tanks require pumping every 3-5 years to remove the solids that have accumulated thru their use. The way a septic tank works is that the waste from your toilets, sinks, showers and laundry enter the tank and bacteria breaks down the organic solids into sludge that settles to the bottom of the tank. Non organic material like plastics, grease, hair and soaps will accumulate in the floating scum layer. If the sludge or the floating scum enters the line that supplies the leach field your leach field will fail. The simple way to prevent this from happening is to have the tank pumped and not to flush anything that isn’t human waste or toilet paper.
Visit our article on How to maintain a septic tank and add a riser
2. Excessive water use.
A leach field is designed to handle a certain amount of water entering the system per day. The way a leach field is designed is by the designing architect or engineer will order a perc test done for the area the leach field is going to be placed. What a perc test does is finds out how much water the soil type will absorb in a specific time. This will determine the size and type of leach field will be required for your house. A 1 bedroom house will have a lower occupancy and use less water and require a smaller leach field than a 3 bedroom house on the same site.
To find out what is involved and how to do a perc test check out our article on
“How to do a perc test” (comming soon)
List of things that your leach field was not designed for
- leaking faucets
- Toilets that don’t stop running
- Sudden toilet usage from additional guest (weekend party or wedding reception)
- Sudden increase in consecutive laundry loads
- Addition of sump pump or gutters to the system
- Draining a hot tub or pool into the system
The failure of the leach field may only be temporary with the leaking toilet or faucet, the saturated field will return to normal after you stop the leak.
Check out our article Why does my toilet run and how to stop it
The failure of the leach field will become permanent if the sudden flow of water into the septic tank stirs up the sludge on the bottom and the particles flow into the leach field and stop the soil from absorbing the water by forming a film or what I call black slime in the field on the soil. If this black slime is formed then you will need to replace the field.
3.Trees or landscaping 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 wide open spot but don’t do it. The tree or shrubs nature is for its roots to travel and find moisture. They will naturally travel too and enter the leach line pipes. The pipes have holes running along the bottom and that is where the water flows to enter the leach field and this is where the roots will enter. The roots will completely stop the flow of water in time and the leach field will need to be replaced. I have seen this many of times. The best trees to plant on your leach field is no trees.
4.Driving over the leach field with autos or heavy equipment
Driving over a leach field damages the field by:
- compacting the soil
When the soil that the leach field is compacted by heavy tire trafic the absorption rate is affected in a negative way. When the soil gets compacted there is no easy way of repairing it other than remove the affected soil and replace it with new soil.
- Damage the pipes by crushing or breaking them
When the tires drive over the leach field lines, more so when the ground is wet, there is a good chance that the pipes may be crushed or moved and the joints separated. The pipe joints are not glued in a leach field. If the pipe gets crushed or a joint separates then that pipe will no longer work causing a field failure. The crushed or separated pipe is repairable by digging up the affected area and repairing the crushed or separated spot.
- Forcing soil into the stone reserve layer
The way a leach field lateral pipeline is constructed is by digging a trench approximately 20 to 24 inches wide and to the depth that the design calls for. The trench has 6 inches of 2 inch washed stone placed in it then the pipeline with the holes on the bottom and more stone until you get a 6 inch coverage over the pipe.
The stone provides empty spaces between them that act as a reservoir for the water until the soil absorbs it.
Then a filter is placed over the stone before soil is placed over it. Fabric or straw is used to hold back the soil. When you drive over the field when it is wet you may damage this filter and allow the upper soil to filter into the stone filling the reservoir. The only fix for this is replacing the leach field.
5. Building a parking area on the leach field
Building a parking lot on top of the leach field damages it by:
- Compacting the soil
- Prevents the evaporation of the water
The second way the leach field removes the water that you put into it is by evaporation. When you cover the field with material to park on you will reduce or stop the evaporation process causing the failure of the field. Removing all the material involved and replacing it with new permeable material is the fix. This is very expensive to do.
6. Raising the soil level over the leach field with fill dirt
Leach fields are designed to work at a certain depth. When you bring fill material and raise the ground level there are two things you are going to accomplish
- Compact the soil
- Stop the evaporation
Your field may work for a short period of time but when it fails to repair it you will need to build a new field at the new height and possibly install a lift station to get the water up to the new field.
7. Change in the water drainage plane
The drainage plane is the way the water from rain flows across the ground. You have seen how a low spot in a yard or field has standing water in it after a heavy rain. The same thing could happen to your leach field and this would be bad for your leach field to have happen.
If you have any landscaping work done it should not drain to the leach field. The same goes for your roof gutter downspouts. They should not drain into your leach field.
The water from a rain should always run away from your leach field for it to operate efficiently.
8. Building a storage shed, pool or patio on the leach field
Building any of these has the same effect as building a parking lot on top the the leach field.
Soil compaction
Evaporation reduction
The system may never fail completely but the system will not work as designed after the construction. Best not to build on it.
9. Distribution box failure
The distribution box is connected to the pipe that comes out of your septic tank and directs water to each of your leach field lines. The leach field has multiple lines. The soil type and the number of bedrooms will determine the number of lines designed into it.
The distribution box can be made out of cement, plastic or steel. Steel ones are not common. The common ones are plastic and cement.
Distribution boxes normally fail when something heavy drives over top of them and the box gets crushed. You may not notice that it got broken. If it breaks it could fill up with soil and stop the distribution of water to the leach field lines. This is a easy fix by replacing the broken box with a new one.
10. Septic tank failure, exit pipe falls off
The way a septic tank is constructed is that the waste water and solids come into the tank and are directed down into the center part of the tank (approximately 12 inches or so) by a elbow or a tee acting as a elbow.
The tee is much smarter way of doing it so it can be cleaned if it gets clogged with grease or soap.
The exit pipe is the same setup except that the area it draws from is a few inches lower than the tee that supplies the tank. This configuration reduces the chance that raw sewage will make it into the leach field creating a failure.
The exit pipe are glued in place and the problem occurs when the glue fails and lets the elbow or the lower pipe drop off. Then raw sewage flows into the field and the black slime starts growing and you will get leach field failure. I have repaired fields that this has happened.
The bad news is, there is not much you can do to prevent this from happening.
The good news is it does not happen that often.
I hope this article has helped answer your question, here is a bonus that fits into this article.
How long does a leach field or drain field last
This is a question that has no set answer. A drain field or leach field should last between 30 to 50+ years. It depends on the soil type, if the septic tank properly maintained, and if the field was designed and installed correctly.
I built my house in 1984 and the leach field is still working as designed. My parents house has 50 years on the leach field and it has no problems. I have seen leach fields last for 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 soil type, how it was designed and maintained and if any of the above article circumstances occurred.
Best wishes
Gary 10/11/2018
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