A septic tank system (also called an on-site sewage disposal system) is a disposal system for water and household wastes from the kitchen bathroom, and laundry.
The system provides initial treatment of these wastes before they are further purified by the filtering action of the soil. The septic tank and drainfield are the system’s two main components. The septic tank is a large underground storage tank which is usually mad of concrete. However, some tanks are made of other materials such as fiberglass or plastic. The tank collects and holds all of the household wastes for two to three days, so that the heavy suspended materials such as feces, food residues and soils sink to the bottom to be decomposed by bacteria into sludge. Lighter materials such as grease and paper products float to the top and form a scum layer, which is trapped in the tank by baffles. The scum also decomposes in time. After being partially purified, the waste, water flows from the septic tank into the drainfield. At that point the wastewater is called “effluent.”
The drainfield is a network of perforated pipes buried underground in gravel trenches. The effluent flows through the pipes out the holes and into a large area of soil. The soil is an excellent filter, removing the remaining suspended substances, pollutants and bacteria from the effluent. A small amount of effluent taken up by grass and nearby trees is evaporated.