Causes of Septic Drainfield Failure

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Septic System Drain Field Failure

90% of septic system failures are caused by
Drain Field Failure

septic system drain field, distribution box and septic tank

The septic drain field, or drainfield, also known as the leach field, 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 drain field soil to absorb water. When absorption stops it results in drainfield failure.

Septic Drainfield Problem #1 - The Biomat

The bio mat is a naturally occurring tar-like substance that forms on the bottoms and sides of the drain field 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 and form an impermeable layer. As these aerobic colonies die off they leave behind sulfides, which over time will clog soil passages and stop absorption.

Septic Drainfield Problem #2 - Sodium Bonding

A commonly overlooked problem develops in soil containing clay. Sodium in ordinary detergents, soaps, household cleaners, and water softeners causes clay particles in the soils to chemically bond and turn into hardpan.

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 drain field failure.

When a drain field 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.

Septic Drainfield Problem #3 - Crushed or Broken Drain Pipes

Placing a septic drain field in an area where it may be driven over is not a good idea. The drain pipes in the gravel bed of a septic drain field can be broken by the weight of a vehicle rolling over the drainage bed. Repeated driving over the bed can also compact the gravel filling the trench reducing its ability to absorb water.

Septic Drainfield Problem #4 - Root Intrusion

Trees and shrubs planted near a drainfield can clog drain field soil. It is important to select non-intrusive species when planting on or near a septic drain field. Plants, such as annuals, perennials, bulbs and ornamental grasses are generally the best choices for use on a septic drain field. Check my blog for more information on planting near a drain field.

If you suspect root intrusion is causing a problem products are available at your local home improvement store that can dissolve the root matter in the drain field without killing the plant. We suggest a foaming type of root killer.

Septic Drainfield Problem #5 - Neglect

This may be the most common cause of septic system failure. Septic tanks must be pumped periodically. Most authorities recommend every 3 - 5 years. Septic solids should remain in the septic tank and pumped on a regular schedule. If a tank is not pumped, sludge accumulation can cause solid organic materials to be transmitted to the drain field 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 drain field where, over time, they will clog soil pores.

Avoid problems: have your tank pumped regularly by a licensed septic service company.
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