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The Causes of Septic System Drainfield Failure InspectAPedia®  -     Causes of septic system drainfield or leachfield failures, how to recognize & diagnose failing conditions in a septic field Definitions of septic failure for each component

This chapter discusses 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"?

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.

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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)

• 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.

• 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 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 pation on top of a septic drainfield
  • Don't pave over the septic drainfield
  • Don't put outdoor carpeting over a septic 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
• 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.
  

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  SEPTIC FIELD FAILURE CAUSES
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  SOIL CONDITIONS
  PLANTS OVER SEPTICS
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WHAT CAN GO INTO TOILETS & DRAINS?

• Biomat Formation in the drainfield - what is it, why do we need it?

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More Information on Building Diagnostic Inspections and Repairs

• 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 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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