In a typical household today, waste from household plumbing, such as sinks, showers, toilets, and laundry, flows through pipes into either a sewer or an on-site wastewater treatment system. The typical on-site wastewater treatment system used by rural homeowners consists of two stages: the first is a septic tank, which is followed by a septic drain field (also known as a leach field or soil absorption system).
The purpose of a septic tank is to retain the solid waste and keep it from flowing out into the septic drain field. In a properly operating system, only the liquid from the tank is allowed to seep into the soil through the septic drain field. To help keep solids from flowing from the tank, some newer systems incorporate septic effluent filters for filtering the water as it leaves the septic tank.
Depending upon the requirements of your local public health authority, septic tanks are usually constructed from either concrete or fiberglass. Occasionally, homeowners in older homes may discover that a steel tank was used for this purpose. However, due to concerns about the steel tanks rusting through, they are usually no longer permitted.
Septic tanks are normally full of liquid and waste all the time. Most septic tanks have three basic layers of waste, as shown in the diagram below:
Scum, which includes debris such as grease, settles at the top and floats on the liquid. Liquids will settle in the center, while heavier solids settle to the bottom. As shown above, the influent and effluent pipes are designed so that their openings are in the area of the tank normally containing liquids - this helps to keep solids and scum from entering the septic drain field. As new waste and liquids enter the system, the liquid near the center of the tank is pushed out into the septic drain field.
Septic tanks need to be pumped on a regular basis to remove the accumulated solids and other debris. The frequency of the required cleaning will be dependent upon the size of the tank and the number of people living in the home. A typical family of four with a 1250-gallon septic tank will normally need to pump the tank every 3 - 4 years.
The liquids pushed from the septic tank normally flow into a septic drain field (or soil absorption field). The typical septic drain field contains a series of perforated pipes buried in trenches. The purpose of a septic drain field is to treat the liquids by removing contaminants and other impurities from the liquid as it passes through the trenches surrounding the pipes. Homeowners in older residences may have systems such as cesspools or tanks connected to drywells or seepage pits, but many public health officials no longer permit such systems to be used.
Although the typical septic system, when properly maintained, can operate efficiently for many years, problems do sometimes occur.
Many septic system failures are obvious, such as toilets or drains backing up into the home or liquids appearing on topic of the soil where the tank or drain field is located. These problems can be caused by clogged or broken pipes, cracks in the septic tank, or a saturated drain field. Some of these problems can be corrected by the homeowner, while others may require the assistance of a professional.
The use of garbage disposals in homes with septic systems can also lead to problems for homeowners. Pipes can become clogged with food, and due to the increased solids, it is normally necessary to have your septic tank pumped more often if you choose to use such a device.
Avoid driving over your septic tank or drain field, as this weight of your vehicle can compress the soil and potentially cause the tank or drain pipes to crack. Also, do not cover these areas with cement, blacktop, or other materials that may interfere with the soil's natural ability to absorb and filter liquids.
If you have a private well, it is important to keep your septic system away from your well area. Otherwise, it is possible for bacteria and nitrates to enter and contaminate your drinking water source. For this reason, most public health departments have minimum distance requirements that homeowners must maintain between their wells and septic systems.