Roughly one-quarter of all American homes disposes of their wastewater through onsite (unsewered) systems. Using such systems, individual homeowners are responsible for the treatment and disposal of their own wastewater. Most are typically located where centralized wastewater treatment is unavailable or impractical, such as in rural areas. The most popular onsite method currently in use is the septic system. Septics use the soil to treat small wastewater flows. When properly constructed and maintained, septic systems both are reliable and safe.
Although there are numerous types of septic systems available, all operate using the same general means. A typical system consists of a septic tank, a distribution box, and a rock-and-gravel-lined absorption field (also known as a drain- or leach field). All of these components are connected by pipes called conveyance lines.
Tanks are normally constructed of concrete, fiberglass or plastic, and are usually of a size large enough to hold a minimum of 750 to 1000 gallons of sewage. The tank's purpose is to temporarily contain the wastewater as solids and liquids separate. The solids (known as sludge) sink to the bottom of the tank, while scum floats on top of the liquid. The sludge and scum remain in the tank and must be pumped out periodically (generally every 3 to 5 years with a properly working system). The liquid wastewater, commonly called effluent, passes on through the tank to the distribution box. The distribution box channels the effluent into a network of perforated underground pipes in the absorption field, where it passes through holes in the pipes into the field. There it's stored until absorbed by the soil. The absorption field treats the wastewater through physical, chemical and biological processes, effectively filtering it before it reaches the ground water.
When installing a septic system, the main factors to consider include the size of the lot, the depth of the soil and its percolation rate (how quickly it absorbs water), and the depth to the seasonal high water table levels. If building on a parcel of vacant land, it's also wise to determine the best location for the septic system before deciding on where to put your house and well. The required installation process can vary from state to state, and even from county to county, so contact the area's local zoning department for advice.