A typical system contains a septic tank, a distribution box, and a rock-and-gravel-lined absorption field, sometimes called a drain field. All are connected by pipes called conveyance lines.
Tanks are made of concrete, fiberglass, or plastic. They usually are buried, and should be watertight. Most are designed to hold a minimum of 750 to 1000 gallons of sewage. The tank’s purpose is to temporarily hold the wastewater until solids and liquids separate. The solids, known as sludge, collect at the bottom of the tank, while scum floats on top of the liquid. The sludge and scum will remain in the tank and need to be pumped out periodically.
The wastewater, or effluent, will pass through the tank to the distribution box. The distribution box separates the flow of the water into a network of underground, perforated pipes in the absorption field. The effluent passes through the hopes in the pipes into the rock-and gravel zone. It will be stored there until it is absorbed by the soil.
The absorption field treats the wastewater through physical, chemical, and biological processes. The soil acts as a natural buffer to filter out bacteria, viruses, and excessive nutrients. If a septic system is designed, constructed, and maintained properly, the wastewater is treated before reaching the groundwater.