Cause of Septic System Failure

The purpose of a septic system other than the Pirana® is to recycle and purify the water component of sewage on the property where the sewage originates. This is done by the three components of a septic system essentially by filtration. Learn about the three parts and function of your septic system and what causes failure below.

Basic Septic System Overview


A filter is defined as an appliance, apparatus, device or process that removes a portion of any stream of material passing through it. That defines how the three parts of a septic system work. The first filter is the anaerobic septic tank (no oxygen in the water); the second filter is the construction of the disposal field; the third filter is the native soil surrounding the disposal that provides the final treatment.

First Filter

Sewage enters an anaerobic septic tank as solids carried in water. Human intestinal bacteria and microbes in the feces survive in an anaerobic septic tank. They become suspended in the water. The bacteria breakdown the solids in the water into two layers: settled sludge on the bottom and floating solids on the surface. Eighty to ninety percent of solids are retained in the septic tank in these two layers. The water between these two layers contains vastly reduced numbers of problem intestinal bacteria and microbes, soluble organic material and fine suspended particulates. The contaminated anaerobic water leaves the septic tank and flows to the disposal field. This separation and retention of solids is filtration.

Septic Tank and Filtering Basics

Second Filter

The contaminated anaerobic water from the septic tank enters the disposal field. The anaerobic contaminated water slowly moves through the disposal field allowing some of the soluble organic material to coagulate and settle to the bottom of the disposal field along with suspended particulate matter, including bacteria and microbes, forming another kind of sludge. The water with reduced contamination is then absorbed by the surrounding native soil. This process is filtration.

Septic Field Bed Basics

Third Filter

Septic Field Bed Over Time

The twice filtered contaminated anaerobic water is absorbed by the aerobic native soil surrounding the drain field.

After passing through three to five feet of undisturbed aerobic native soil the water will be purified by the soil pores capturing and holding the remaining soluble organic matter, particulates, bacteria, and microbes in the contaminated water. The surfaces of the undisturbed native soil in the disposal field capture the highest concentration of the soluble organic matter, particulates and bacteria, and microbes. Anaerobic intestinal bacteria colonize these infiltrative surfaces. They secrete a black slime layer called 'biomat.' The biomat slime also filters and holds organic matter, particulates, and microbes. This entire process is filtration.

Failure is caused by biomat slime. Biomat slime clogs the soil pores in the infiltrative surfaces of the disposal field inhibiting the movement of water into the native soil. The bottom of the disposal field clogs first. Eventually a small portion of the contaminated water can't be absorbed each day. Contaminated water collects in the bottom of the disposal field. Where the contaminated water contacts the side walls of the disposal field, intestinal bacteria colonize these surfaces secreting more clogging biomat. The liquid depth of the contaminated water in the disposal field rises. Over years and decades, the biomat clogs all of the infiltrative surfaces of the drain field and the drain field fills with contaminated water. Failure occurs. Biomat is the cause of 95% of septic system failures.

Common Septic System Problems

Failure has a number of common symptoms:

1) Soft, damp soil over the disposal field or septic tank.

2) Wet spots or standing water over the disposal field or septic tank.

3) Slow draining toilets or not draining at all when they are flushed.

4) Sewage coming out of the shower or tub drain when the toilet is flushed.

Foul, nasty odors occur with most failure symptoms.

Before the Pirana®, the only solution to a failed septic system was to replace the disposal field. Increasingly, complicated engineered treatment systems are required that cost tens of thousands of dollars more. These engineered systems are so inefficient they still require the three filters after adding an aerobic process between the first and second filter. Since 2000, the Pirana® has provided the only certified cost-effective alternative to this expensive and damaging solution.

Contact Pirana® System and learn about solutions to common septic system problems.
For more immediate information on septic system failure click on REPORTS AND INFORMATION below