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SEPTIC DRAINFIELD LIFE
SEPTIC FAILURE CRITERIA
SOIL CONDITIONS
PLANTS OVER SEPTICS
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- 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
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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.
© 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.
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)
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- 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.
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- 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.
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Driving 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 shown here, 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.
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- 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?
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