What causes a septic system failure?

This septic system diagnosis article explains the causes of septic system failure in the drain field, leach field, seepage bed, or similar component.

We list the causes of each type of septic component failure, and list the septic component failure criteria or in other words what conditions are defined as "failure"?

We also discuss what can be planted over and near a septic drainfield and what should be avoided.

How can you distinguish between a blocked pipe, a septic tank that needs pumping, and a clogged drainfield that needs replacement? This is an important question as it distinguishes between relatively low cost maintenance or repair task and a costly septic leach field replacement.

Septic Absorption Field Failure Causes: what ruins septic drainfields, leaching beds, soakbeds, or soakpits?

Here is a list of the causes of sewage wastewater disposal field failures. These factors explain why soakaway beds, seepage beds, leach fields, disposal fields, drainfields, or other synonymous effluent treatment & disposal systems fail early or at the end of a normal life.

• Septic Drainfield Age:
  
  eventually even a well-maintained SAS will eventually clog and have to be replaced.
  
  Just how quickly depends on several factors including original construction type, materials, and quality, field size, septic system usage level, soil characteristics, soil water or groundwater control, and of course septic tank pumping frequency to avoid sending solids into the fields.
  
  But for all systems that depend on disposal and treatment of wastewater in the soil, the biomat that forms around drainage trenches, seepage beds, or soakbeds, cesspools and soakpits eventually clogs.
  
  The reason for [septic absorption ] system failure is the gradual formation underground of an imperable clogged or crusted layer in the soil blow and surrounding the seepage bed.
  
  Flow of water through this clogged or crusted zone is severely restricted or even eliminated, although the permeability of the surrounding soil remains essentially unchanged.
  
  Consequently, huge voumes of stagnant septic tank effuent accumulates in the seepage bed. - Harkin (1975)
  
  See SEPTIC DRAINFIELD LIFE
  
  and SEPTIC LIFE EXPECTANCY where we also discuss septic tank life and other septic component life.

Nevertheless a number of additional factors can hasten the demise of a septic soakbed or leachfield.

• Septic Tank Pumping schedule:
  
  don't forget to pump out the septic tank regularly (solids/grease are discharged into the fields, clogging the soil).
  
  
  • Soil clogging at the biomat layer 
    
    which forms below and around the drainfield trenches (or other absorption systems). The biomat is a bacteria layer which forms in soil below and around drainfield trenches where septic effluent or wastewater is discharged.
    
    This biomat layer is critical in the processing of fine biological solids and pathogens which are in the effluent, and without it the septic system would not be adequately treating the effluent. Inadequately-treated effluent released into the ground risks contamination of nearby ponds, wells, streams, etc.
    
    The formation, clogging, and measures to protect and extend the life of the biomat
    
    See BIOMAT FORMATION & SEPTIC LIFE
• Septic Tank Baffle failures:
  
  corrosion and rust-off of steel septic tank baffles is a significant cause of disposal field failure in systems that have otherwise been maintained by proper tank pumping schedules.
  
  Concrete or plastic tank baffles also fail, break, or fall off; baffles can be repaired or replaced but the drainfield may already have been damaged and its future life reduced.
  
  See SEPTIC TANK BAFFLES for details.
• Blocking or sealing the ground surface over a septic drainfield will be a problem 
  
  over just about any septic effluent absorption field. Don't build anything over a septic mound, no building, no fish pond, no patio, no tennis court, no parking area, no playground (compacts the soil).
  • Don't put a swimming pool
    
    on top of a drainfield - yes I've seen people do this including my neighbor! See the photo at the top of this page.
  • Don't put a concrete block patio
    
    on top of a septic drainfield
  • Don't pave over the septic drainfield
    
    with cement, asphalt, bricks, or anything else.
  • Don't put outdoor carpeting
    
    over a septic drainfield
  • Don't put plastic weed barriers such as weed barriers over the drainfield.
  • Don't install astroturf™
    
    or other synthetic groundcovers over a septic drainfield unless a careful review with the product manufacturer assures that the cover will not interfere with moisture evaporation from the soil below and oxygen entry into the soil below
  • Don't build a building or deck
    
    on top of the septic drainfield - you risk damaging the drainfield during construction by equipment, by breaking pipes, by digging into a pipeline, and you prevent future access and repair to the drainfield
  • Don't seal the drainfield or soakaway bed top from contact with air by leaving a plastic liner of any sort -
    
    ice rink, swimming pool, tents and tarps in place. Temporary placement of such sealers, depending on weather conditions and temperatures, may not be harmful, such as during solid freezing conditions, but we have not found independent research that confirms or denies the problem.
    
    For example, details of the pros, cons, & warnings about building a temporary ice rink over septic fields are found
    
    at ICE SKATING OVER SEPTIC
• Driving vehicles or any heavy equipment over the absorption system,
  
  leach field, drainfield. As with any septic absorption system, heavy traffic over the system can compress soil or break pipes, rendering the system inoperative and requiring costly repairs.
  
  At a recent inspection I found that the septic mound had been placed over a roadway connecting two properties owned by the same family. Family members continued to drive back and forth between homes right over the septic mound. Its future life was rather doubtful.
  
  Driving vehicles over the septic mound or other drainfield, even for a single project such as construction of a nearby structure or performing other site work, is likely to damage the system and lead to need for costly repairs.
  
  Kahn et als. also advise keeping grazing animals, horses, cows, etc. off of mound systems.
  
  In the photo above on this page, light snow makes it quite apparent where someone has been driving through this field. Compacting the soil by driving over the drainfield will damage it and may lead to early failure.
  
  Details are at DRIVING or PARKING OVER SEPTIC
• Septic tank converstion to aerobic or aerator systems without proper design,
  
  components, or installation.
  
  Simply dropping an aeration system into a conventional septic tank, particularly a single-chamber septic tank will virtually guarantee that suspended solids will be sent into and then destroy the leaching fields. Settlement chambers, septic filters or an equivalent will be needed when converting from a conventional to an aerobic septic system design.
  
  See CONVERT to AEROBIC SEPTIC SYSTEM
• Septic tank or field construction mistakes:
  
  Improper original construction by bad site selection , especially on rocky, poorly-drained sites (pipes settle, for example) including improper trench grading & routing or extending piping over variations in trench grading without proper bedding (causing pipe settlement).
  
  Inspecting raised bed and mound systems in New York State I have often seen improperly constructed mounds including efforts by the builder to save on fill cost by using the "mound" as a place to first pile up all of the trees and tree stumps which needed to be cleared from the site, covering this mess with a too-thin layer of fill soil in which the septic absorption trenches are installed.
  
  The result is a mound system with a short life. If you see trees poking out from the perimeter of your mound further investigation may be in order. Also watch for effluent breakout around the bottom edges of the mound.
  
  Driving over the septic drainfield trenches during construction, omitting the required gravel under and around drainfield trench piping, and possibly backfilling with heavy wet clay-based soils during construction may also damage the field or reduce its performance.
  
  See our warnings at (3) CONSTRUCTION of SHALLOW SEPTIC SYSTEM Absorption Trenches
• Shortcuts by the drainfield constructing contractor or excavator such as
  • Failure to provide proper type & quantity of gravel in drainfield trenches - hasty backfill with available soil
  • Failure to install drainfield trenches of depth, length, width, slope specified by the septic system designer & planner
• Soil clogging at the biomat layer
  
  which forms below and around the drainfield trenches (or other absorption systems). The biomat is a bacteria layer which forms in soil below and around drainfield trenches where septic effluent or wastewater is discharged.
  
  This layer is critical in the processing of fine biological solids and pathogens which are in the effluent, and without it the septic system would not be adequately treating the effluent. Inadequately-treated effluent released into the ground risks contamination of nearby ponds, wells, streams, etc.
  
  

  The formation, clogging, and measures to protect and extend the life of the biomat is discussed

  at BIOMAT FORMATION & SEPTIC LIFE

• Houses clustered around a lake:
  
  often will have a marginal system as properties were crowded together, built as part-time summer-camps, were built without code supervision, and often were built using amateur, marginal home-made systems.
  
  In our photograph (left), new construction placed the septic tank and septic drainfields in the wet area shown in the photo.
  
  Everything looked questionable: the drainfield is placed near trees, risking root invasion of the piping; the drainfield is placed in wet soils, and the total elevation between the bottom of the drainfield piping and the top of the nearby lake is less than two feet. The drainfield is placed less than 20 ft. from the edge of the lake.
  
  It is improbable that the septic system belonging to this property will do much more than contaminate the nearby lake.
• Improper septic absorption field location:
  
  one way to have a quick failure of a drain field is to install it in an area of high seasonal water tables (flooding the system) without sufficient fill and elevation, and/or without providing extra site and intercept drainage around the field to keep surface and subsurface water away from the field.
• Surface & subsurface runoff water control mistakes:
  
  Ignoring site runoff and groundwater levels: Improper absorption field siting is found at some properties where the builder fails to consider site runoff or natural groundwater paths.
  
  One mound system was constructed using too little fill and placed over what had been a stream bed.
  
  My septic dye test very quickly produced red-dyed effluent at the low end of the mound where a seasonal stream continued to run under the mound in wet weather. Flooding the absorption system with surface or roof runoff, or rocky, poorly-drained or under-sized sites may simply lack capacity means a short absorption field life.
• Steep slope septic systems:
  
  Placing a conventional septic system drainfield on a steep slope, over a stream bed, over a natural drainage swale (photo of this defect), specifying an under-sized mound or raised bed for the anticipated usage level, and poorly installed piping which does not slope properly or which becomes disconnected,
  
  and finally, use of improper fill soil which lacks the proper percolation rate all result in a costly installation with a too-short life.
• Sloppy pipe layout and connections is a common cause of early failure in new drainfields.
  
  Pipes placed in trenches at uneven slope become disconnected; trenches with improper slope and omission of the specified amount and improper placement of gravel (for those systems) are also quite common where there is time or money pressure working against the builder.
• Placing structures, patios, or paving over the absorption system:
  
  Covering an absorption bed, raised bed, or septic mound, such as by installation of paving, a patio, or weed-blocking solid plastic,
  
  will damage the mound and prevent proper operation by blocking both oxygen intake into the soil and also evaporation of effluent from the soil top. See "Blocking the ground" earlier in this list.
• Placing improper substances into the building drains and septic system.
  
  Don't use the septic system to dispose of illegal oils, chemicals, fats, greases. One system in New York near the Taconic State Parkway was connected to house in which was operated an illegal drug manufacturing operation.
  
  So much contaminant was flushed down house drains that the workers contaminated their own well and poisoned themselves.
  
  See TOILETS, DON'T FLUSH LIST
• Discharging excessive salts or other chemicals which destroy the the biomat formation, clogging the soil. This problem and measures to protect and extend the life of the biomat is discussed at "Biomat Formation".
  
  See REDUCE IMPACT of SOFTENER on SEPTIC
  
  and
  See BIOMAT FORMATION & SEPTIC LIFE
• Planting trees, deep rooting shrubs, and certain ground covers 
  
  on the septic absorption field (roots enter pipes) and evaporation can be blocked.
  
  See SEPTIC SYSTEMS, PLANTS OVER
• Use of septic tank or drain field additives 
  
  which claim to extend system life can generate so much activity in the tank that solids are held in suspension and forced into the soil absorption system! While not all septic treatments harm the system some do, and expert, authoritative sources advise that these treatments are at best un-necesssary and at worst cause expensive damage.
  
  Do not add any treatments, chemicals, yeast, or other treats to a septic system. In general these treatments don't work, may ruin the system, and are illegal in many localities. There is no magic bullet to repair a bad SAS.
  
  See SEPTIC TREATMENTS & CHEMICALS
• Wet weather installations of septic systems & fields:
  
  Installing a drainfield in wet weather (which compacts the soil) is likely to mean a shorter field life.
  
  See SOAKBED SOIL CONDITIONS

Research on Avoiding Soakaway Bed Failures

• Harkin, John M., Michael D. Jawson, and F. G. Baker, CAUSES AND REMEDY OF FAILURE OF SEPTIC TANK SEEPAGE SYSTEMS [PDF] University of Wisconsin, 1975.
  This text explains the reasons for soil clogging and septic drainfield failure. - Ed.
  
  The reason for [septic absorption ] system failure is the gradual formation underground of an imperable clogged or crusted layer in the soil blow and surrounding the seepage bed. Flow of water through this clogged or crusted zone is severely restricted or even eliminated, although the permeability of the surrounding soil remains essentially unchanged.
  
  Consequently, huge voumes of stagnant septi tank effuent accumulate in the seepage bed.
• Jenssen, P. D., and R. L. Siegrist. "Technology assessment of wastewater treatment by soil infiltration systems." Water science and technology 22, no. 3-4 (1990): 83-92.
• Jnad, I., B. Lesikar, G. Sabbagh, and A. Kenimer. "Soil clogging in a subsurface drip drain field." In On-Site Wastewater Treatment, p. 18. American Society of Agricultural and Biological Engineers, 2001.
• McGauhey, P. H. "Manmade Contamination Hazards a." Groundwater 6, no. 3 (1968): 10-13.
  Abstract:
  
  Hazards to ground water may result from adding to water which may infiltrate the soil, or to the soil through which water percolates, wastes from man's life processes; his industrial and commercial activity; or his use of water, fertilizers and pesticides in agriculture.
  
  From experimental data it is evident that particulate matter, including bacteria and viruses, do not move far with percolating water in a soil system. The chemical products of biodegradation of organic wastes, however, with a few exceptions such as phosphates, move quite freely and hence reach ground water.
  
  Since they are no different than the compounds found in ground waters the effect of domestic use of water is generally to increase the concentration of salts normally present in such waters.
  
  From the vast spectrum of compounds produced by the chemical industry and used in industry and commerce comes hazards to ground‐water quality such as metal ions, phenols, tar residues, brines, and exotic organics which may through accident, carelessness or waste‐water discharge contaminate ground water.
  
  Mineralization with nutrients and soluble soil fractions, and possibly, pesticide residues are the hazards from agricultural use. Leaching from solid waste landfills is possible under poor long‐term management and might involve chemicals, iron, and various earth minerals.
  
  It is concluded that the most serious hazard is the buildup of dissolved solids to levels inimical to beneficial use.
• McGauhey, Percy Harold, Ray B. Krone, and J. H. Winneberger. "Soil mantle as a wastewater treatment system." (1966).
• US EPA ONSITE WASTEWATER TREATMENT SYSTEMS MANUAL [online copy, free] Top Reference: US EPA's Design Manual for Onsite Wastewater Treatment and Disposal, 1980, available from the US EPA, the US GPO Superintendent of Documents (Pueblo CO), and from the National Small Flows Clearinghouse.
  
  Original source http://www.epa.gov/ORD/NRMRL/Pubs/625R00008/625R00008.htm Onsite wastewater treatment and disposal systems, Richard J Otis, published by the US EPA. Although it's more than 20 years old, this book remains a useful reference for septic system designers. U.S. Environmental Protection Agency, Office of Water Program Operations; Office of Research and Development, Municipal Environmental Research Laboratory; (1980)
• Also seeReferences or Citations at the end of this document.

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Reader Q&A - also see RECOMMENDED ARTICLES & FAQs

On 2020-07-19 - by (mod) -

Thanks for a helpful question, Brad.

If there is too much fill over a septic field you deprive the soil bacteria of oxygen. The result is that half of the two types of bacteria (aerobic and anaerobic are the two) can't do their job of breaking down sewage pathogens.

The result of that is that even if you are successfully disposing of effluent you're not successfully treating it. Ultimately such a system contaminates groundwater and nearby wells or water sources. And you may also see a reduced drainfield life.

In fact, the very process of adding backfill over an existing septic drainfield may itself destroy the drainfield by the weight of vehicles carrying soil and dumping and grading it out: compressing the soil and/or breaking pipes.

On 2020-07-19 by Brad

What issues arise from putting too much fill over a septic field? I am constructing a new house and the septic system was installed without any thought to the eventual elevation changes we'd be brining to the site. As a result the "completed" drainage field is many feet lower than the expected grade. If additional fill was brought in how would the system possibly be compromised?

On 2020-07-11 - by (mod) -

Cassie

That describes a failed drainfield

Dirt can get into the drain lines as a result of:

- broken piping anywhere along the line

- tree root invasion

- improper original construction with insufficient gravel around the pipe OR in soil with many fine particles, omission of an appropriate geotextile above the drainline trench during backfill

And standing water in the remaining line tells us that the drainfield area is saturated, not accepting effluent, and thus is not functional;.

Sorry to say it's almost certainly time for a new field. (Just clearing the pipes will give but short relief and is IMO a waste of money on a failed leach field)

On 2020-07-11 by cassie

2 of the three lines are full of dirt, one has standing water. What would be the cause of a dirt filled line? Can moles be a culprit?

On 2020-05-24 - by (mod) -

Sarah

That can work in some (not all) situation, and is certainly not "illegal": directing surface runoff away from a drainfield and installing subsurface drainage trenches around the field to intercept and remove subsurface groundwater can help dry out the drainfield area.

But I'm not optimistic. If the area is one of wet soils we can be trying to remove more water than is feasible.

A local septic engineer who knows various designs, has done a soil perc test, and knows what designs the local septic authority will accept is someone who could be helpful in the case you describe.

As Mark Cramer (Tampa FL home inspector) says: ... it depends.

In this case it depends on local site conditions: terrain shape, drainage, water levels, etc.

On 2020-05-23 by Sarah

he had the installer come and look at everything, and (this is according to my father-in-law passing on the info to me), the field has some sort of "barrier" around it to keep groundwater out. There is some kind of berm at the end of the field that was really high or something (not sure), but either way, the grey water from the field had nowhere to drain.

So the installer is going to charge him $1000 to dig a drainage trench to go even farther somewhere and drain into the trench (which will be filled with stone or sand or whatever it is that's supposed to go in a trench).

I asked him to get a copy of the plans, showing his current setup, and the proposed work.

This does not sit right with me. Is that even legal to have a "barrier" around a leach field?

On 2020-05-22 - by (mod) -

The bottom of a drainfield trench needs to be 2 ft. above the seasonal high water table for a septic system to work, so i agree with you.
And no, the failure may not be obvious right away.

On 2020-05-22 by Sarah

they also live in a very boggy area. Is it possible that the wrong septic system was installed (ie, they should have had a mound system)? Or would that mean that would have had issues right away?

On 2020-05-22 - by (mod) -

Yes that failure cause is likely. As you infer, stirring the septage increases passage of clogging solids into the drainfield.

On 2020-05-22 by Sarah

My father-in-law has a saturated leach field. It's less than 5 years old. He took the (bad) advice of a septic pumper and was adding Septobac (bacteria/enzymes) to his septic system. He also stirred up the first tank every 4 months. He does have an effluent filter. He also did have solids and sludge make it into the second tank (where there should be only water). Is it possible that his actions caused his leach field to clog? Would Septobac and stirring the tank cause a leach field failure within 5 years? It's just him and my mother-in-law who live in the house.

On 2019-12-13 - by (mod) -

Unfortunately constant septic tank pumping never fix a failed leachfield (and cost you plenty).

In wet swampy terrain we often find that when the septic tank is pumped water flows backwards from the saturated drainfield into the septic tank, re-filling it in a day or so - it's basically a waste of money to pump in this case.

I don't have a low-cost solution. What's needed when a septic field was improperly built in the first place, locating it in ground that is seasonally (or always) flooded or wet, is to abandon that drainfield and construct a raised-bed septic or mound system.

Until that's done, what's happening is that each time you flush a toilet sewage effluent is in essence being discharged to the ground surface.

On 2019-12-13 by Linda Shull

We bought a house built on a piece of swampy land. We have had trouble with our septic system every since we moved in. Especially in the winter. Our house was built in 79.

We had the tank pumped and have been adding rides monthly. Is there anything else we can do. We are both retired and living on a very limited income so can't afford any thing really costly. Thank you .

On 2019-07-28 - by (mod) -

On 2019-06-26 by Gkw44 - Nostoc commune is an algae - not quite a fungus

Moderator comment: this septic field failure report discusses the presence of Nostoc commune, a cyanobacteria algae like growth over a drainfield that was diagnostic of a drainfield failure. Nostoc looks like bear poop. It's not.

Details are at SOAKBED SOIL CONDITIONS https://inspectapedia.com/septic/Leachfield_Soakbed_Soil_Conditions.php

...

Continue reading  at DRIVING or PARKING OVER SEPTIC or select a topic from the closely-related articles below, or see the complete ARTICLE INDEX.

Or see SEPTIC DRAINFIELD FAILURE CAUSE FAQs - questions and answers posted originally at the end of this article.

Or see these

Recommended Articles

• AEROBIC ATU SEPTIC FAILURE RATES, COSTS
• DISPOSAL vs TREATMENT - getting rid of effluent isn't the same as avoiding contamination
• SEPTIC DRAINFIELD INSPECTION & TEST - home
• PLUMBING DRAIN NOISE DIAGNOSIS.
• SEPTIC DISPOSAL FIELD CLOGGING INSPECTION
• SEPTIC DRAINFIELD FAILURE CAUSES
• DRIVING or PARKING OVER SEPTIC
• ICE SKATING OVER SEPTIC
• SEPTIC SYSTEMS, PLANTS OVER
• SEPTIC DRAINFIELD FAILURE DIAGNOSIS
• SEPTIC FAILURE CRITERIA
• SEPTIC FAILURE LAWSUIT
• SEPTIC FAILURE SIGNS
• SEPTIC FAILURE SPOTS
• SEPTIC ODORS INDICATING DRAINFIELD FAILURE
• SEPTIC TANK GRASS or SNOWMELT
• SEPTIC TROUBLE SIGNS, OTHER
• SOAKBED SOIL CONDITIONS
• SEPTIC DRAINFIELD LIFE
• SEPTIC SYSTEM ODORS
• SEPTIC TANK LEVELS of SEWAGE

Suggested citation for this web page

SEPTIC DRAINFIELD FAILURE CAUSES at InspectApedia.com - online encyclopedia of building & environmental inspection, testing, diagnosis, repair, & problem prevention advice.

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INDEX to RELATED ARTICLES: ARTICLE INDEX to SEPTIC SYSTEMS

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Citations & References

In addition to any citations in the article above, a full list is available on request.

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