Understanding septic systems capabilities and limits is needed to ensure water quality. A septic system is a type of On-Site Sewage Facility and is a self-contained, underground waste-water treatment system. By using natural processes to treat the waste-water on-site, septic systems do not require the installation of miles of sewer lines, making them less disruptive to the environment. A septic system consists of a septic tank, a distribution system and a soil absorption system, also called a drain field. The septic tank is a watertight box, sometimes made out of concrete or fiberglass, with an inlet and outlet pipe. The septic tank treats the waste-water naturally by holding it in the tank long enough for solids and liquids to separate. The waste-water forms three layers inside the tank. Solids lighter than water float to the top forming a layer of scum.
Solids heavier than water settle at the bottom of the tank forming a layer of sludge. This leaves a middle layer of partially clarified waste-water. The layers of sludge and scum remain in the septic tank where bacteria found naturally in the waste-water work to break the solids down. The sludge and scum that cannot be broken down are retained in the tank until the tank is pumped. The layer of liquid flows from the septic tank to the drain field. A drain a series of trenches lined with gravel or sand and below the ground. The drain field treats the waste-water by allowing it to slowly trickle from the pipes out into the gravel and down through the soil. The remaining impurities are trapped and disposed of in the soil. The excess water is eliminated through percolation into the soil, and eventually returning to the ground water, through evaporation, and by uptake through plants and transpiration.
The Center for Watershed Protection notes that septic systems can be effective methods of water treatment, however failures are common in many areas. Even properly functioning septic systems can leak and are not designed to effectively deal with most of the phosphorus and nitrogen load found in the water it treats. Pathogenic fecal bacteria are also a concern. The primary concern for a municipality is proper maintenance of septic systems, and in some cases the total load of partially treated pollutants that can impact local drinking water and wildlife. A solid understanding of septic systems capabilities and limits, and a good government plan is needed to ensure water quality.