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Septic Field Inspection Procedure How to Inspect the Soil Absorption System or Septic Drainfield for Evidence of Septic System Failure SepticAPedia © Enter your search terms Submit search form   Search This Website - InspectAPedia.com

• Types of septic system drain field failure
• Cause of septic system component failures
• Definitions of septic failure for each component

This chapter discusses 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. We also discuss what can be planted over and near a septic drainfield and what should be avoided. Also see Drainfield Location: how to find the septic drain field or leaching bed. © Copyright 2008 Daniel Friedman, All Rights Reserved. Information Accuracy & Bias Pledge is at below-left. Use the links at page left to navigate this document or to go to Other Website Topics. Green links at left show where you are in our document & website.

Use links just below or at the left of each page to navigate this document or to view other topics at this website. Green links show where you are in our document or website.

SEPTIC FIELD INSPECTION
  SEPTIC FIELD FAILURE CAUSES
  DISPOSAL CLOGGING FAILURES
  DISPOSAL vs TREATMENT
  SEPTIC DRAINFIELD LIFE
  SEPTIC FAILURE CRITERIA
  SOIL CONDITIONS
  PLANTS OVER SEPTICS

SEPTIC FIELD FAILURE CAUSES - Septic Absorption Field Failure Causes of drainfields and leaching beds

• Improper original construction , especially on rocky, poorly-drained sites (pipes settle, for example)

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 the photo shown here, 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 field construction: 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.
• 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.
• 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.
• Installing a drainfield in wet weather (which compacts the soil) is likely to mean a shorter field 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.
• Failure to pump the septic tank on 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 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 Septic System Absorption System Biomat Formation as a subchapter of this text.

• 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. Blocking or sealing the ground surface 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.
• 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
• 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".
• Planting trees, deep rooting shrubs, and certain ground covers on the septic absorption field (roots enter pipes) and evaporation can be blocked. See Plants over Septics
• 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! 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.
• Age: eventually even a well-maintained SAS will clog and have to be replaced.

More Reading:
Biomat Formation in the drainfield - what is it, why do we need it?

Contents

DISPOSAL CLOGGING FAILURES - Effluent Disposal and Drain Clogging Failures

In simplest terms, there are two visible septic effluent or onsite wastewater disposal failures:

• Toilets or other fixtures back up into the house - but first see "Diagnosing Clogged Drains then return here using your browser's "BACK" button.
• Effluent or sewage appears at the surface of the yard, or the neighbor's yard!

Septic odors may also indicate a system failure or an imminent failure. But such odors may also be produced by defects in the plumbing vent system or other site conditions. Beware, sewer gas contains methane and is explosive if it reaches a dangerous concentration inside a building.

Typical causes range from things that are easy and cheap to repair, to a need for complete system replacement:

• Clogged pipes
• Broken pipes
• Damaged tank
• Tipped distribution box
• Clogged/broken soil absorption piping
• Clogged absorption soils (grease & solids)
• Saturated soil absorption area

DISPOSAL vs TREATMENT - Successful Wastewater Disposal Does Not Necessarily Mean Successful Treatment

However there can also be treatment failures. Effluent may not back up or appear on the surface, but if insufficiently treated effluent reaches a private well or any stream or waterway, the environment is being contaminated -- an unacceptable condition. Historically many people have just worried about disposal. As the quality of drinking water deteriorates in many areas and as population grows in many previously thinly-populated areas, proper treatment has become the real concern for everyone's health.

For example, if there is not sufficient soil between the bottom of the soil absorption system trenches and the local groundwater, the local environment is being contaminated.

DRAINFIELD LIFE - What destroys or shortens the life of the absorption system?

I've seen drain fields still working fine after 25 years and others which failed in the first week of occupancy of a new home. In a properly designed septic absorption field the level of usage of the system, site characteristics such as slope, rock, groundwater level, and soil percolation rate have all been considered. Barring foulups such as we discuss in this document, such a field may last from 10 to 20 years. But it's easy to ruin or shorten the life of a drainfield/leaching bed. Review the causes of septic field failure discussed at Field Failure Causes

FAILURE CRITERIA - Soil Absorption System Failure Criteria

• Breakout of effluent observed (& I consider odors as well)
• BOH evaluation in MA if within 100 ft of surface water supply
• within Zone 1 of a public well
• within 50ft of a private well
• between 50ft and 100ft of a private well if well fails bacteria test.

SOIL CONDITIONS - The Drainfield: Leaching Bed Soil Condition & Liquid level

The absorption system or "drain field" has two jobs. First, it disposes of liquid effluent by permitting it to seep into the soil below. Second, a "bio-mat" of bacteria which forms in the soil below the drainage field processes pathogens in the septic effluent to make the effluent sufficiently sanitary as to avoid contaminating nearby ground water. This distinction between successful "disposal" and successful "treatment" is important to avoid groundwater contamination but has not been addressed by regulation in every municipality. Municipalities which require a minimum distance between the bottom of the drain field trenches (or equivalent component) and the top of the seasonal high ground water table have recognized the importance of a working bio-mat and the need to provide adequate dry soil for it to function.

Even in a well-designed drainage field, eventually the soil surrounding the drainfield device (perforated pipe in gravel trench or other seepage system) becomes clogged with grease and debris. Examining an excavated cross-section of a failed drainfield will often display a black or gray band of sludge and grease of about 1" thickness at the inside perimeter of the gravel trench. When this layer of soil becomes sufficiently clogged the passage of effluent into the soil below is slowed and eventually blocked, leading to the need for replacement. Keeping a tank pumped so as to reduce the passage of debris and grease into a drain field will extend its life.

This is the most expensive problem to correct. Look for septic effluent seepage to ground surface in area of equipment or downhill from such equipment. Look for (illegal) drain field line extensions to nearby streams, storm drains, or adjoining properties where the temptation to "fix" a failing system by sending the effluent to an improper destination overwhelmed a previous owner or repair company. In some areas inspectors use septic loading and dye test. Seepage may be due to overloaded tank, failed absorption system, or blocked/broken piping (may be less costly).

An excavator or septic contractor will often explore one or more drain lines (or similar components) by excavating a portion of it to look for evidence of flooding or soil clogging. We've used a simple probe at the end and along a leach bed to check for flooding of that component. (Be careful not to break or collapse old piping.)

More Reading:
Soil Percolation Tests or "perc tests" are used to evaluate the ability of the soil to absorb effluent. Normally this test is done at the time the absorption system is being designed or to obtain a board of health approval on the leach field location. However a perc test may also be performed during the evaluation of an existing septic drainfield. Soil percolation tests are discussed in more detail at the Soil Percolation Testing chapter.

Planting Guidelines for Septic Drainfields, Mounds, Raised Beds, and other Septic Absorption Systems

Planting grasses or flowers over septic fields

Many people have written to ask me what can be planted over a septic field. Grasses, weeds, flower are OK: The best answer is grass or native grasses and weeds. Flowers are ok so long as they are not varities which send down deep roots. Basically, any shallow-rooting planting will be ok over the surface of a absorption field or over most other septic drainfields.

Planting Trees or Shrubs Near or Over Septic Absorption Systems

Stay away from trees or shrubs which are likely to put down deep roots. The roots will quickly invade and clog the buried effluent lines and may also cause them to move, break, or become disconnected. Some experts (Kahn, Allen, Jones) also point out that if you're planting on the edges and lower toe of a septic mound, those plants need to be able to tolerate the higher moisture levels found in those parts of the mound system.

Trees are not OK: Kahn, Allen, Jones (book cited at Septic Systems Home-References) that trees such as bamboo, willow, eucalyptus, cypress, Monterey pine, pepper, and walnut have particularly aggressive and deep roots. Keep such trees at least 100 feet from the septic field.

Planting Ground Cover Over Septic Fields

Ivy, Pachysandra, Similar Ground Covers are NOT OK: these plants will reduce effluent evaporation from the mound soils and because their roots often invade and clog effluent distribution piping.

The Septic Systems Online Book - Where Are We?

More expert information on this topic

More Information on Septic System Diagnosis, Maintenance, & Repair

• The Septic System Information Website home page for this topic
• Septic Systems Inspection, Testing, & Maintenance- online textbook. Detailed how to inspect, maintain, repair information
• The Home Buyer's Guide to Septic Systems
• Septic Tank Pumping Guide: When, Why, How to pump the septic tank
• Tank Location - How to Find the Septic Tank, how deep will the cover be, how to document its location
• Drainfield Layout: septic drainfield or leaching bed shape and placement considerations
• Drainfield Layout: septic drainfield or leaching bed shape and placement considerations
• Drainfield Location: how to find the septic drain field or leaching bed
• Home & Outdoor Living Water Requirements
• Septic Tank Capacity vs Usage in Daily Gallons of Wastewater Flow, calculating required septic tank size, calculating septic tank volume from size measurements
• How Big Should the Leach Field Be? - table of soil percolation rate vs. field size
• Septic System Drainfield Absorption System Biomat Formation - what leads to drain field clogging and expensive drainfield repairs
• Table of Required Septic & Well Clearances: Distances Between Septic System & Wells, Streams, Trees, etc.

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