90% of septic system failures are caused by
DrainField Failure
Failure Of The Drain Field, Absorption Field, Leachfield
Many factors can contribute to drainfield failure. Structural problems such as clogged or broken pipes can lead to visible failures. Pipes can be broken or clogged by tree roots, by construction activities, or by cars driven over drainfields. However, a system need not be physically broken to fail. Septic solids remain in the septic tank and must be pumped on a regular schedule. If a tank is not pumped, sludge accumulation can cause solid organic materials to be transmitted to the drainfield where they can clog soil passages and cause over growth of the bio mat. Additionally, grease and fats that form a floating layer in the septic tank can be emulsified by soaps and detergents. These tiny particles of fat and grease can then flow to the drainfield where, over time, they will clog soil pores.
The drainfield, also known as the leachfield, absorption bed, disposal field or seepage field performs the task of accepting and processing wastewater, or effluent, from the septic tank before it returns to natural aquifers below the earth's surface. All systems rely on the ability of the drainfield soil to absorb water.
 A typical drainfield
is gravity fed. It usually consists of several gravel-filled trenches with perforated drainpipe buried just below the surface of the gravel running the length of the trenches. The effluent is distributed, usually through a distribution box, to the various lateral drainpipes exiting through the perforations into the surrounding gravel bed. Secondary processing begins in these beds as the effluent fills the trench then percolates through the bio mat and into the surrounding soil. There are many other configurations commonly in use.
 Infiltrator® systems
are more recent technology. Infiltrator chambers are hollow structures that attach end-to-end. They are installed in trenches or beds without gravel (except where local codes require the use of gravel). The entire bottom of the
trench is open for unobstructed infiltration of water. The large storage volume within the hollow chambers accommodates peak flows of effluent from the home. Infiltrator chambers also feature patented sidewall louvers that allow lateral leaching of effluent into the soil.
 Mound Systems
On problem sites, mound systems may be an alternative. In a mound system, septic tank effluent is delivered to the mound through the use of a pump in a dosing tank placed after the septic tank. The mound itself is carefully constructed above ground using specially selected sand placed on top of the natural soil to help treat and dispose of septic tank effluent. The depth of sand is determined by the depth of the natural soil above a limiting layer. A limiting layer can be bedrock, a soil layer with a very low percolation rate, or seasonally high groundwater. The depth of sand added to the depth of the natural soil must equal the minimum treatment depth prescribed by local authority.
The bio mat is a naturally occurring tar-like substance that forms on the bottoms and sides of the drainfield trenches. It is made up of living anaerobic (without oxygen) organisms, which feed on organic matter in the wastewater. As the bio mat matures it grows thicker slowing down the flow of wastewater to the surrounding soil. As the wastewater passes through the bio mat pathogenic organisms and viruses are removed. On the outside of the trench, beyond the bio mat where the soil is not saturated, are living colonies of aerobic (with oxygen) bacteria. These aerobic bacteria colonies feed on the bio mat and keep it from becoming so thick that wastewater will no longer pass through.
When soil floods these aerobic bacteria colonies will die off and no longer keep the bio mat in check. The bio mat will grow too thick and drainage will stop. Further, as these colonies die off they leave behind sulfides, which over time will clog soil passages stopping the flow of water. When the bio mat grows too thick a waterproof barrier develops and absorption stops.
Another common problem develops in soils containing clay. Sodium in ordinary detergents, soaps, household cleaners, and water softeners causes clay particles in the soils to chemically bond.
To learn if your soil has a high clay content take a handful, dampen it, then squeeze. If the soil sticks together in a clump it has clay in it. The more solidly it sticks together the more clay.
When soil absorption stops, soils flood. Standing water may be seen on the surface of the drain field. Water may back up into the tank and even into household plumbing. This is often the first sign of soil failure in your septic system. Drain field soils begin failing at the beginning of the field. As areas of soil clog the effluent moves to the next available area down the line, when water reaches the end of the field, and can no longer be absorbed, it surfaces. This is a sign of total drainfield failure.
When a drainfield fails water will run back to the tank after the system is pumped. A visible sign is water puddling on the surface of the field. There may be a septic odor around your house or backyard. Drains may run slowly or have an odor.
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