A septic system is a highly efficient, self-contained, underground wastewater treatment system. Because septic systems treat and dispose of household wastewater onsite, they are often more economical than centralized sewer systems in rural areas where lot sizes are larger and houses are spaced widely apart.
Septic systems are also simple in design, which make them generally less expensive to install and maintain. By using naturally occurring bacteria processes to treat the wastewater onsite, usually in a homeowner’s backyard, septic systems don’t require the installation of miles of sewer lines, making them less disruptive to the environment.
The conventional septic system is composed of two basic components, a septic tank (for solids and scum) and a tile bed for effluent to drain into.
Some treatment of the waste occurs in the septic tank (where liquids are separated from solids and to provide some breakdown of organic matter in the wastewater). The layers of sludge and scum remain in the septic tank where bacteria found naturally in the wastewater work to break the solids down, referred to as an aerobic process (largely without oxygen). The sludge and scum that cannot be broken down are retained in the tank until the tank is pumped.
The septic tank is a buried, watertight container made from concrete, polyethylene or fiberglass. The size of the septic tank is determined by the size of the house (as well as number of bedrooms and fixtures) to determine the amount of household water use, to calculate a daily design sewage flow based on Part 8 of the OBC.
The partially treated wastewater from the septic tank flows into the leaching bed or to a distribution device, which helps to uniformly distribute the wastewater in the leaching bed. A conventional leaching bed (also known as a drain field, disposal field, or a soil absorption system) is a series of in-ground absorption trenches or a bed lined with gravel or course sand and buried one to three feet below the ground surface. Perforated pipes or drain tiles run through the trenches to distribute the wastewater. The leaching bed treats the wastewater by allowing it to slowly trickle from the pipes out into the gravel and down through the soil. The gravel and soil act as biological filters. The majority of the treatment occurs in the tile bed where oxygen is introduced to the wastewater via the soil, and aerobic bacterial treatment occurs in the soil and in the gravel bed.
Conventional septic fields include filter beds and raised absorption trench fields.