How does a septic system work?

A septic system treats household wastewater on your own property. Water from toilets, sinks and laundry flows into a buried, watertight tank, where solids settle as sludge and grease floats as scum. The partly treated liquid then flows into a drainfield, a set of shallow trenches or beds in unsaturated soil, where it soaks through the ground. The soil does the final treatment, removing bacteria, viruses and nutrients before the water reaches groundwater. Because the soil is part of the treatment, its type, depth and drainage decide whether a site can use a conventional system or needs an advanced design such as an aerobic unit.

Sources

• How Septic Systems WorkU.S. Environmental Protection Agency
• Onsite Wastewater Treatment Systems: Septic Tank/Soil Absorption Field (L-5227)Texas A&M AgriLife Extension Service