SEPTIC effluent BREAKOUT in the yard, or odors, is a sign of a problem with the soil absorption system Signs of Septic System Failure
Step by Step Septic Problem or Failure Diagnosis

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What is considered a septic system or soakaway or drainfield failre? Are there failure criteria? Yes.

How Does Each Septic System Component Fail? What to Look For During a Septic Inspection - Step by Step Diagnosis of Septic System Failures, clogged drains, odors, sewer backup, wet areas in the yard, and slow drains.

This septic system inspection article describes detailed "how to" steps instructing the septic inspection investigator in how to inspect specific septic components for signs of failure.

We describe the criteria for saying a septic system has failed, and we take you step by step through the onsite waste disposal system, from the building to tank to absorption system, with suggestions for examining the condition of each component so that a proper diagnosis of the cause of septic failure and a specification of the appropriate repair can be made.

In the photo at the top of this page, a wet spot appeared in the previously "perfect" yard of this older home within twenty-four hours of the new family moving-in. The buyers had obtained a "septic inspection" but it was improperly performed and missed the chance to discover before purchase that the septic system was in total failure.

We also provide a MASTER INDEX to this topic, or you can try the page top or bottom SEARCH BOX as a quick way to find information you need.

SYSTEM FAILURE CRITERIA - Septic System Failure Causes: What Constitutes a "Failed" Septic System?

Photograph of septic tank baffles

Before digging up your septic tank or calling a septic pumper, if you think the septic system is failed because of drain blockage or drains backing up into the building, you should to see CLOGGED DRAIN DIAGNOSIS & REPAIR Is it a blocked drain or the septic system? - A First Step for Homeowners.

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Article Contents

Onsite Waste Disposal System Failure Criteria

Massachusetts Title 5 Septic Law lists specific failure criteria and serves as a good model for septic inspections anywhere.

(The photograph shows the septic baffles in a concrete septic tank. While at the time of inspection the sewage was not flowing over the baffles, sewage debris atop the concrete baffle shows that at some point that problem had occurred. Further diagnosis was in order.

Detailed criteria that define when a septic system has failed can be read at SEPTIC FAILURE CRITERIA.

Septic Piping Failures Between Building Drains and the Septic Tank

Photograph of new septic line house to tank

Outside, waste piping conducts sewage (black water and gray water) from the building to the treatment tank or "septic tank," and from the treatment tank to the distribution box. Our photo shows a new waste line carrying sewage down from the home to the septic tank in lower yard. The previous waste line had been broken when driven over by a heavy lawnmower.

Septic drain lines between the house and the septic tank should be of solid, non-perforated material and need to be protected from mechanical damage (such as by vehicles).

Piping extending from the distribution box into drain fields is normally perforated, though solid lines might be used if effluent is being processed by more specialized devices such as seepage pits, galleys, or a sand-bed system.

Distribution piping connects the house drain to the septic tank, running between the building and the tank inlet.

More distribution piping connects the septic tank outlet to the distribution box and from there to the leach field. Distribution pipes can settle (especially in new construction), break, become blocked or clogged, or become invaded and blocked by tree roots or soils.

Older ORANGEBURG PIPE which look like black asphalt-soaked cardboard (they are) crush and deteriorate with age.

Clay pipes also break and have a tendency to become blocked by tree roots at their joints. You won't know what kind of piping is installed until it is excavated, but the age of the property may be a clue. Homes built from the 1970's on, certainly from the 1980's on, use cast iron or more often plastic ABS or PVC piping for these connections.

This line may become blocked by waste, damaged by collapse of a section, or invaded by roots. Detection of these conditions is fairly easy by routing a snake or power snake from the building drain to the septic tank.

An experienced power snake operator can often tell by "feel" that a drain line is collapsed, partially collapsed, or invaded by roots. While you may make a temporary "repair" of such a condition by drain-cleaning, if the line is broken or root-invaded, you should expect to have to excavate and replace it soon.


How Different Types of Septic Tanks Fail

Photograph of  rusted out and dangerous steel septic tank Photograph of  rusted out and dangerous steel septic tank

How to Find The Septic Blockage

The same failures can occur on the effluent distribution pipe line from the septic tank outlet in to the distribution box as we described earlier on piping from house to the septic tank.

Pipes can settle (especially in new construction), break, become blocked or clogged, or become invaded and blocked by tree roots or soils.

How to Determine Where a Septic Blockage Is Located

How would we distinguish among blockages at different points in these distribution lines?

Septic System D-Box Failures: What Goes Wrong at the Septic System Distribution Box

Photograph of a septic system distribution box

Distribution boxes serve as a connection point to distribute effluent which arrives from the septic tank outlet and is to be sent into two or more individual leach field lines.

Distribution boxes ("D-Boxes") can settle or tip.

A damaged or tipped D-box will fail to divert effluent uniformly among the effluent receiving drainfield lines, causing flooding of one leach line. If you see depressions suggesting that there are four leach lines at the property and the end of just one of them is producing wet soil or surface-breakout of effluent, we'd suspect a tipped D-box.

Opening the D-box can also show whether or not effluent is being directed uniformly into each of the leach lines. A tipped D-box can overload one line and cause early failure of the absorption system.

If this is happening, flow adjustment end-caps (eccentric holes) can be installed in the distribution box on the inlet end of each of the drain lines, permitting adjustment of effluent delivery into each line, perhaps relieving the problem line and redistributing effluent into the others.

Septic Drain Field Piping - Diagnosing Leach Field Failures

costly surprise caused by building a swimming pool over the drainfield

In a conventional "drain field" (synonyms: leachfield, leaching bed, soakbed, soakaway bed, seepage bed) of perforated pipes buried in gravel-filled trenches, a drain line may be invaded by tree roots. This is why experts advise keeping tree and shrub plantings away from drain fields.

Vehicle traffic can also collapse this or any outdoor waste piping, which is why experts advise against ever driving over a drainfield or over any other septic system components.


Drainfield piping is usually constructed of perforated pipe buried in gravel-filled trenches. It receives effluent from the D-box and allows it to percolate or seep into the soil around the trench where added filtering and bacterial treatment occur.

Like the distribution piping discussed above, individual drainfield pipes can become crushed, shifted, or clogged by tree roots or other debris. More general clogging and failures of the leach field are discussed below.

A broken or clogged pipe, once it has been located, may be much less costly to repair than a complete leach field replacement, so this possibility needs to be considered during diagnosis of a "failed" septic system.

Lockwood, in "An Engineer's View of Septic Systems" listed these causes of absorption field failure:

" If the liquid effluent cannot soak into the soil surrounding the leach field, sewage may back up into the system and overflow into the house or puddle on the surface of the ground. There are several possible causes for this problem."

  1. Poor Soil Conditions: Faulty Design or Installation of Septic Systems A leaching system placed in unsuitable soil, a system that is too small for the house it serves, or an improperly constructed system may lead to early failure.
  2. Soil Clogging and Septic Systems: If sludge or scum is allowed to escape into the distribution box and from there into the leach field, the soil will quickly become clogged. If this happens, the liquid will no longer soak, or percolate, into the soil.

    This condition can be caused by broken baffles in the septic tank that allow sludge or scum to escape.

    Failure to have the tank pumped can also lead to a situation where the sludge and scum overwhelm the baffles.

    If a steel septic tank has rusted out and collapsed you should assume that before the collapse it was releasing solids and grease into the absorption system, reducing its life.
  3. High Water Table and Septic Systems: During wet, or abnormally wet, seasons groundwater may rise into the leach field and force sewage upward to the ground surface.

    This condition may mean the system has to be re-installed at a higher level. It may also be possible to intercept the high groundwater with a series of drains around the system called "curtain drains".
  4. Roots and Clogging of Septic Systems: The roots of trees and bushes planted too close to the system can sometimes enter and block the pipes of the system.

    Removal of the plants and clearing the pipes of the roots is usually required.
  5. Physical Damage to Septic System Components: Trucks or heavy equipment passing over the system can damage pipes and joints to the point of rendering the system inoperable. You should be aware of the location of the system and direct traffic to avoid such damage.

These pages are part of our SEPTIC DYE TEST PROCEDURE for testing septic system function.


Continue reading at DRAINFIELD RESTORATION APPROACHES or select a topic from closely-related articles below, or see our complete INDEX to RELATED ARTICLES below.

Or see SEPTIC FAILURE INDICATOR FAQs - posted originally at this article


Or see these

Septic Drainfield Failure Inspection Articles

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


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