What is a Septic System?

A septic system is made up of a tank and a drain field. It is designed to treat and dispose of domestic wastewater through a combination of natural processes. When properly installed and maintained, a septic system can render wastewater ecologically safe.

Why are Septic Systems Necessary?

Safe treatment and disposal of domestic wastewater protects public health and the environment while preventing drinking water pollution and the spread of disease.

Connection to a wastewater treatment facility is not always available (i.e. rural areas, small communities).

How Does a Septic System Work?

1. Household wastewater is flushed.
2. Wastewater flows into the septic tank.
3. Heavy and light solids are broken down by bacteria that reside in the septic tank and form the scum and sludge layer.
4. Wastewater flows out of the tank into the drain field (the scum and sludge layers remain in the tank).
5. In the drain field, wastewater is absorbed by the soil and is broken down by natural processes.

Septic systems, like private wells, are the homeowner's responsibility. An improperly used or maintained septic tank system can affect an entire community by causing one or more of the following problems: a breeding area for mosquitoes and other insects, undesirable odors, costly damage caused by sewage backing up inside the home, the spread of serious diseases, and pollution of groundwater, wells, rivers, and lakes.

How to Apply for a Septic System Permit?

For information on how to apply for a septic system permit, please visit our Permits, Licenses, and Reports page.

South Carolina's Challenge

Some septic systems fail to work properly, usually because of poor maintenance. Don't let yours be one of them — learn how your septic system works and how to care for it.

How a Septic Tank System Works

Parts of a Septic Tank System

The most common type of septic system has four main parts:

1. An exit pipe that carries wastewater from the home to the septic tank and vents noxious gases up and out of the house
2. A buried, watertight septic tank made of concrete, fiberglass, or polyethylene, usually installed about 6 feet from a home
3. The drain field, which consists of one or more distributor boxes and a network of pipes buried in relatively shallow trenches that are usually packed with gravel or other filler
4. Soil is full of bacteria that digest most contaminants before wastewater reaches groundwater.

How it Works

Household wastewater is flushed or washed through the exit pipe into the septic tank.

Heavy solids sink to the bottom. Over 24-48 hours the solids break down to form a sludge layer. Lighter floatable solids, such as grease, oils, and fats, collect at the top of the liquid in the tank to form a scum layer.

The bacteria that live in the septic tank constantly break down solid waste. The tank's fittings hold the scum and sludge from flowing out into the drainfield.

Liquid that is washed or flushed into the tank is known as effluent. In the tank, effluent is partially treated or "clarified" by bacteria. As the tank fills up, the liquid empties into the drainfield, where it is absorbed into the soil.

The liquid drains through the soil layers, where bacteria filter and digest contaminants. By the time the wastewater reaches groundwater, it is fully treated.

Additives

Companies that make and sell biological additives sometimes claim that their product restores a septic tank's bacterial balance, and that this is necessary as part of a routine monthly maintenance program. But bacteria already reside in human feces, so these additives usually are not necessary.