Septic Problems: Drainfield
Learn the signs and symptoms of common drainfield problems and failures: Learn how to
diagnose the soil absorption system and how
a few simple steps will help avoid the headache and high costs
associated with leach field problems.
Discover the solution to correct problems and steps to prevent them from
Drain Field Problems
Septic tank problems cause and lead
to drain field problems.
The drain field is where the waste water goes after it leaves the septic tank , also called leachfield or disposal field. It can also go to a mound, a seepage bed , or a seepage pit . The general and more technical term for all these methods of handling the wastewater from the tank is the soil absorption system. We will begin with the most common type, the
drain field or leach field.
Once sewage undergoes primary treatment in the septic tank, the clarified effluent flows to the drainfield,
where it is discharged into the soil for final treatment and disposal.
A typical drain field consists of several relatively narrow and shallow gravel-filled trenches with a perforated pipe near the top of the gravel to distribute the wastewater throughout each trench. In most cases,
drain fields will perform indefinitely if an effective septic aerator is installed
RIGHT cross section of a typical drainfield.
The Biomat The natural occurring process of wastewater entering your leach
field, drain field,
mound, seepage bed , or a seepage pit is the formation of the biomat.
The biomat (biological mat) comprises of a black, jelly-like mat that builds on the bottom and sidewalls of the drain field trench.
It is composed of anaerobic (without oxygen) microorganisms (and their by-products) that attach themselves to soil and rock particles. Their food is the
organic matter in the septic tank wastewater. Because the biomat has a low permeability, it retards the rate of flow out of the trench
into the drain field soil.
The Beginning of
Drain Field Problems
The biomat builds first of all along the trench bottom then upwards along the trench walls.
It has less permeability than fresh soil, so incoming wastewater will pool over the biomat
and drip along the trench bed to an area where there is little or no biomat; eventually the
biomat will line the bottom of the trench and form up along the walls as well.
Along the soil side of the biomat, in a non failing or problem drain field, aerobic soil
bacteria (microorganisms that consume both organic matter and oxygen)
feed on and break down the biomat. In ideal conditions, these two processes go on at the same time, so the thickness and the ability of the biomat to filter waste water
stay fairly consistent
LEFT cross section of a drain field that is in the early stages of failing.
Aerobic(with oxygen) soil bacteria no longer consumes the biomat at the same rate as the biomat grows.
A number of things can contribute to a drain field becoming saturated. Failure to pump regularly, soil compaction, or a
wide range of abuses homeowner put on their septic system. In a saturated environment, the anaerobic organisms in the
biomat feed on the organic material in the wastewater; this causes the biomat to grow thicker and decreases the rate of
diffusion of a effluent into the drain field.
Testing Your Drain Field for Potential Problems|
Lush lawn and plant growth or soft wet spots over the drain field (or tank) are sure signs of
septic problems. One way to
check the drain field's absorption capacity is to run a hydraulic load test: run 50 to 80 gallons of water into the tank and,
with the outlet riser or cover open, watch how long It takes to drain into the drain field A slight back-up from the normal
tank water level (the bottom of outlet pipe) is OK. The water level may rise 1\2 to 1 inch, but if the field is unclogged
and doesn’t have excessive biomat growth, a fully-flooded tank should drop to normal levels in five to ten minutes.
Drain Field Problems = Failing System
Since the biomat is alive, its balance can be upset.
Septic tank problems can result in an
excess of organic material (food) to the biomat organisms, causing excessive growth and, therefore,
reduced the ability of the waste water from the septic tank to penetrate the
biomat and enter the ground. In the saturated state the soils aerobic conditions no longer exist, and controlled breakdown
of the biomat by aerobic soil bacteria will no longer occur .
RIGHT Cross section of a failing drain field caused by
The biomat has grown too thick and dense, and the effluent sent to the drain field
will quickly and easily exceed the amount that can filter through the biomat.
The result is excessive ponding in the trenches, backflow into the septic tank
(and possibly also into the house), and surfacing of effluent above ground over the drain field causing
wet spots and rapid grass growth, in other words "septic system failure."
Septic Aeration Restores Drain Fields
The waste in a septic system breaks down when naturally occurring anaerobic
bacteria consume the organic material in sewage. Anaerobic microorganisms grow
only in the absence of oxygen. Adding a septic aerator encourages the growth of
living, active aerobic bacteria as a means of treating effluent. These aerobic
microbes are the reason septic aeration works so well. Aerobic microorganisms
are far more robust and effective then anaerobic. As shown in image on the left,
aerobic bacteria (microorganisms that consume both organic matter and oxygen)
are 50 times larger than anaerobic bacteria. When dissolved oxygen is introduced
(septic aerator), microorganisms in decomposing organic matter consume oxygen
dissolved in the water. The more dissolved oxygen the septic aerator can
introduce the more aerobic microbes can live to consume organic matter.
Studies have shown anaerobic microorganisms only break down 60 to 70 percent of solids in a septic tank,
while aerobic microorganisms break down 90 to 98 percent of solids.
Adding a septic aerator to your system causes aerobic bacteria (microbes) to digest wastes in the tank. The microbes also travel into the drainfield, where they digest the biomat which grows and survives only in an anaerobic
(bacteria that grow only in the absence of oxygen) environment.
Effective Septic Aeration Pays for Itself in Pumping Costs|
It is widely recommended that septic tanks be pumped every two to five years. However, recent studies indicate that
adding a septic aerator to a well functioning tank, may result in only having to pump it every 10 to 12 years. Septic
tanks without aeration break down approximately 60 to 70 percent of the solids. Whereas, adding effective septic aeration
breaks down 90 to 98 percent of solids and at a much faster rate.