How does a basic septic system work?

A septic system is built to treat the waste from your home by separating the solids and liquids, then dispersing the liquids in the soil where they can be treated naturally.

Figure 1 shows a typical septic tank. On the left is the inlet pipe — This is where the waste enters the tank. Over time, the solids sink to the bottom and becomes sludge, and the water and scum rise to the top. At the top right, you can see a riser with the access port to pump the accumulated sludge out of the tank.

Figure 1 shows a properly maintained tank with good proportions of water and sludge. On the right is the outlet pipe which runs to the drain field. The outlet pipe usually has a filter to filter the scum.

Figure 2 shows two common designs for the septic system drain field. The partially treated wastewater flows into the perforated pipes, which run through trenches or across the bottom of a bed. There is usually sand underneath the pipes which allows everything to dissipate and bacteria to grow and break down the wastewater even further.

The pipes are then covered to help protect the treatment process. Failure to maintain any portion of this system, especially the tank itself, can lead to a number of problems, including contamination of your private well, septic backup in your house, or untreated waste overflowing in the drain field. That’s why we at the Private Well Class consider septic system maintenance to be an important part of your water system responsibilities.

The Private Well Class is a collaboration between the Rural Community Assistance Partnership and the University of Illinois through the Illinois State Water Survey, and funded by the United States Environmental Protection Agency. The views expressed here are solely from the class authors and not endorsed or reviewed by US EPA. For more information on private wells, sign up for our free 10-week email course at PrivateWellClass.org.