University of Connecticut Cooperative Extension System: Water Quality and the Home Landscape

Septic System

Components of the Septic System


Karen Filchak


Septic Systems are designed to collect, treat and dispose of wastewater.  They are intended to do this without contaminating our water resources or clogging the soils.  About 40% of Connecticut’s residents rely on a septic system to treat household wastewater.

Why care about all of this?  A malfunctioning or failing system can significantly impact health:  human, environmental and financial.  Understanding how a septic system works and learning the best ways to manage it will help you provide the optimum conditions for the long life of the system.

The septic system has two main components:  the tank and the drainfield.  

The septic tank has three functions:

(1) Separation of solids – settling;

(2) Limited decomposition of solids; and

(3) Storage of solids. 

In the septic tank, the settling (and separation) of the solids is an important function.  Light waste (scum) floats; heavier waste (sludge) settles.  The space between the two is where the wastewater accumulates.  It is the wastewater only (effluent) that is intended to exit the tank and enter the drainfield.  The solids must be routinely pumped to prevent system failure.  A common cause of failure is the passage of solids from the tank to the drainfield, which eventually will result in clogging of the drainfield.  An effluent filter (which can be retrofitted to existing tanks) can reduce the likelihood of solids leaving the tank.  This filter should be cleaned when the septic tank is pumped.  A primary measure of a tank’s effectiveness is its ability to prevent solids from entering the drainfield.

In a properly functioning septic system, up to 80% of solids can be broken down into gases and liquids.  A properly sized tank can 3 – 7 days worth of wastewater to allow for proper settling.    A two chambered tank has been required in tanks installed since 1991 to ensure that adequate settling of solids occurs prior to effluent entering the drainfield.  Baffles in the tank at the inlet and outlet pipes help to slow wastewater as it enters the tank (allowing for less disturbance of the settling process of waste already in the tank) as well as help prevent solids from leaving the tank.

The drainfield consists of trenches or a bed, lined with gravel or coarse sand (recycled products are being tested as alternatives for gravel and sand).  Perforated pipe or drain tiles line the trenches and are buried one to three feet below the surface of the ground.  The wastewater trickles through the pipe, entering the zone of unsaturated soil.  Many harmful bacteria and microbes are filtered out as the wastewater passes through this zone.  Soils differ in their ability to remove pollutants from the wastewater.   The soil’s ability to remove pollutants directly impacts the quality of wastewater entering the groundwater.

A distribution box helps to evenly distribute the wastewater among the drainfield trenches.

Many homeowners use or consider using additives in an effort to extend the life of their septic system or reduce the need or frequency of pumping the tank.  The U.S. Environmental Protection Agency and the Connecticut T Department of Public Health recommend against the use of additives.  Studies have not found additives to provide any real  benefits however some types of additives can actually result in problems.   Chemical additives are ineffective in cleaning the tank or drainfield but can contaminate water.  Biological enzymes have not been shown to have of any value.  Acids can cause a concrete tank to deteriorate. 

The septic tank and drainfield are the two main components of a septic system. Image courtesy of the University of Minnesota's Onsite Sewage Treatment Program.

Septic Systems