How to Diagnose a Clogging Failure of the Septic Drainfield

This article explains how to detect and diagnose a clogging failure of the septic drainfield or leachfield as one of the types 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"?

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.

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Evidence of Septic System Effluent Disposal or Drain Clogging Failures

Septic effluent runs out of the system, across rocks, down the hill (C) D FriedmahIn simplest terms, there are several visible septic effluent or onsite wastewater disposal failures accompanied by several other indicators that the soakaway bed, drainfield, or leaching beds are in trouble:

  • Slow drains are the symptom of septic system field failure that people often notice first, though slow drains can also be caused by drain blockages or plumbing vent defects. If you have to flush a toilet repeatedly to get waste to exit the bowl and provided that the water volume used is normal at each flush, then there's a problem not to be ignored.

    Wait too long and a slow toilet flush becomes a costly sewage backup cleanup project or if not repaired promptly you may face a building flood and mold contamination cleanup project in addition.

    Watch out: pumping the septic tank can give temporary, emergency relief to a slow flush or drain backup problem due to a failing septic system, but depending on the daily volume of wastewater produced, the tank will fill up again in just a few days (or less).

    Pumping the septic tank doesn't fix anything. If you are pumping the septic tank at abnormally frequent intervals the septic system is in trouble and needs repair or replacement. Pumping the septic tank on regular schedule (SEPTIC TANK PUMPING SCHEDULE) can extend drainfield life but if the field has already failed all you obtain is temporary relief - and the ability to flush toilets until the septic tank fills again in 1 to 7 days.

    Sorry but SEPTIC DRAINFIELD RESTORERS? are also not likely to fix the trouble and some contaminate the environment and are illegal in most jurisdictions.
  • Toilets or other fixtures back up into the building when the drain blockage or septic failure is more extreme - but before assuming a slow drain or backed-up toilet is due to a failed septic system, first see CLOGGED DRAIN DIAGNOSIS & REPAIR then return here using your browser's "BACK" button. You may also need to see TOILET REPAIR GUIDE.
Algae at a lake shore traced to failed septic system (C) Daniel Friedman
  • Effluent or sewage appears at the surface of the yard, or the neighbor's yard! (Also called septic breakout or effluent breakout).

    At SEPTIC FAILURE SPOTS we describe where effluent typically shows up when the disposal field is failing.

    At above left we show septic effluent flowing over rock down-hill and some distance from the actual septic tank and seepage pit. You may find evidence of septic failure by improper effluent discharge that is not immediately obvious, such as effluent showing up in a nearby drainage ditch or even as abnormal algae growth in a nearby lake, stream, or pond (photo at left) where high levels of nitrogen in the wastewater encourage an algal bloom like this one.

    When there is an argument about whose septic system has failed, yours or your neighbors, or when we're not sure if the wet area is due to surface runoff or to septic system failure, a septic dye test can sort out the question.


    If you find these conditions the septic system has probably been in failure for some time in that it has not been adequately treating the effluent.
  • Distribution box abnormal conditions: check the distribution box that feeds individual absorption field lines for tipping, effluent back-flow from the fields, solid sewage, or inadvertent un-balanced flow into the various drainfield lines or sections.

  • Greener grass: is the grass greener over the septic tank? Not necessarily, both because soil backfill depth may be less in that location and because while effluent may leak out of a septic tank more often it leaks to the ground surface in the area of the disposal field itself.

    See SEPTIC TANK GRASS or SNOWMELT - melting snow can also show where warmer wastewater is reaching the ground surface.
  • Noises: gurgling burping drains may indicate a septic field failure, though partial drain blockages and vent system defects

    See PLUMBING VENT NOISE that can also cause that symptom. Also see PLUMBING DRAIN NOISE DIAGNOSIS.
  • Septic odors may also indicate a system failure or an imminent failure. Septic or sewer odors are not always noticed when a drainfield has failed nor when drains are clogged. And such odors may also be produced by defects in the plumbing vent system or other site conditions.

    Watch out: Beware, sewer gas contains methane and is explosive if it reaches a dangerous concentration inside a building.
  • Septic tank inspection can also give evidence of drainfield failure such as abnormally high sewage levels in the tank (over the baffles - SEWAGE LEVELS in SEPTIC TANKS) or wastewater re-entering the tank from its outlet during tank pumping


    High wastewater may also be due to SEPTIC TANK LEAKS into the septic tank not just due to a failed drainfield.

    Discovery of very high sludge levels or scum layer thickness (MEASURE SCUM & SLUDGE ) indicates that the tank was not pumped often enough. Failure to maintain enough open or free area in the septic tank pretty much guarantees that solids have been flowing into and shortening the remaining life of the absorption bed or drainfield.

Understand the Cause of Septic Field Failure to Determine What Repair is Needed

Septic drainfield cross section sketchTypical causes of septic system disposal field failure range from things that are easy and cheap to repair, to a need for complete system replacement:

  • Clogged building drain or septic system effluent distribution pipes - see

  • Broken drain pipes or septic effluent distribution piping anywhere in the system, starting between the building and the septic tank or even inside the building.

    and related articles can help trace piping.
  • Damaged septic tank - if the tank baffles are damaged it's easy to replace them, and not costly, but you may have already sent sewage solids out into the drainfield, reducing its future life.

  • Tipped septic effluent distribution box - find and inspect and fix the D-box and you may be back in business. Often a tipped D-box is sending all of the septic wastewater down just a portion of the drainfield, overloading it and causing an apparent failure.

  • Clogged/broken leachfield or drainfield soil absorption piping - find, diagnose, and repair the pipe and you're back in business

  • Clogged drainfield or soakaway field absorption soils around the drainfield piping or trenches, (often by salts, grease & solids, or by an over-aged too-thick biomat) - people try magic bullets, additives, restorers, but despite testimonials and advertising by companies selling these restorers, we have had few reports of lasting, effective success. You may need a new septic drainfield, or you may be able to switch to an alternating drainfield or set of trenches to rest and recover the sluggish section.


    Also see septic drainfield clogging at SEPTIC DISPOSAL FIELD CLOGGING INSPECTION.

    Drainfield soils can become clogged or drainfield pipes can be broken and crushed by driving equipment over the drainfield - see DRIVING or PARKING OVER SEPTIC.
  • Water-saturated drainfield soil absorption area - you may need to replace the entire drainfield, switch to an alternating bed or set or septic fields, or it may be possible to direct surface and subsurface water from other sources away from the drainfield area.
  • Septic Tank Back-Flooding: a flooded septic tank - that is a tank at abnormally high levels or a septic tank that back-floods during or soon after it has been pumped out may explain both sewage backups in a building and might indicate a septic soakbed that is in failure.

    At SEPTIC TANK BACK FLOODING we explain the causes of abnormally high sewage levels in septic tanks.

Septic Drainfield / Soakbed Failure Articles


Continue reading at SEPTIC FIELD FAILURE CAUSES or select a topic from the More Reading links or topic ARTICLE INDEX shown below.

Or see SEPTIC DISPOSAL FIELD CLOGGING INSPECTION - what visual signs of septic failure can be easily observed and what does each mean?

Suggested citation for this web page

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

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