Septic Systems


Nearly 25 percent of the U.S. population—more than 25 million homes—disposes of wastewater through onsite, or unsewered systems. With unsewered systems, homeowners are responsible for treating and maintaining the disposal of wastewater.

The most popular method used is a septic system. Septic systems use soil to treat small wastewater flows. When properly maintained, septic systems are safe and reliable.

How septic systems work
A typical system contains a septic tank, a distribution box, and a rock-and-gravel-lined absorption field, sometimes called a drain field. All are connected by pipes called conveyance lines.

Tanks are made of concrete, fiberglass, or plastic. They usually are buried, and should be watertight. Most are designed to hold a minimum of 750 to 1000 gallons of sewage. The tank’s purpose is to temporarily hold the wastewater until solids and liquids separate. The solids, known as sludge, collect at the bottom of the tank, while scum floats on top of the liquid. The sludge and scum will remain in the tank and need to be pumped out periodically.

The wastewater, or effluent, will pass through the tank to the distribution box. The distribution box separates the flow of the water into a network of underground, perforated pipes in the absorption field. The effluent passes through the hopes in the pipes into the rock-and gravel zone. It will be stored there until it is absorbed by the soil.

The absorption field treats the wastewater through physical, chemical, and biological processes. The soil acts as a natural buffer to filter out bacteria, viruses, and excessive nutrients. If a septic system is designed, constructed, and maintained properly, the wastewater is treated before reaching the groundwater.

Septic system design
Local regulations should always be reviewed before a septic system is installed, according to the National Small Flows Clearinghouse. Such regulations can help make sure that the septic system is:

  • A safe distance from houses, water wells, or other water sources
  • An adequate distance from groundwater
  • Sized properly to handle the estimated wastewater load—both into the septic tank and the drain field.
Proper septic system maintenance
The National Onsite Wastewater Recycling Association (NOWRA) recommends the following septic system maintenance practices:

  • Have your septic tank inspected every three to four years
  • Pump if sludge fills the bottom third of the tank or if the scum layer is near the top of the outlet baffle.

If not inspected periodically and pumped when needed, the tank will fill with sludge and the solids will be washed out into the soil treatment area where they will quickly clog the soil. Newer systems may include an effluent screen near the outlet of the tank. The screen helps remove additional solids and can extend the life of the system. The screen should be routinely inspected and cleaned when needed.

The frequency of pumping depends on a number of factors and can vary substantially between homes from once or more a year to 10 years or more.

Inadequately functioning or failing septic systems
According to the National Small Flows Clearinghouse, inadequately functioning and/or failing septic systems can contribute to the contamination of groundwater. Wastewater from septic systems may include many types of contaminants, such as nitrates, harmful bacteria, and viruses.

Signs that wastewater from your septic system could be reaching water sources include:

  • Wastewater backing up into household drains.
  • Bright green, spongy grass on the drain field, even during dry weather.
  • Pooling water or muddy soil around your septic system or in your basement.
  • A strong odor around the septic tank and drain field.

If you notice any of the preceding symptoms, call a septic professional to inspect your system.

Septic system dos and don’ts
  1.  All wastewater may go to the system, though “greywater” (wastewater other than from the toilet and kitchen sink) can be used for purposes as state or local regulations allow.
  2. Conserve water to avoid overloading the system, and repair leaky faucets and low-flow fixtures
  3. Don’t use the system as a trash can for disposal of things other than what’s normally household wastewater–i.e. grease, disposable diapers, paper towels, paint, pesticides
  4. Plant only grass over and near your septic system to avoid root systems that can clog and damage the absorption field
  5. Keep roof drains, sump pump drains, and other rain or surface water drainage away from the absorption field as flooding can keep soil from naturally cleansing wastewater
More info:
Some state agencies have a mechanism in place to assist homeowners with repair/replacement of failing septic systems, while others do not. For more information, contact your state regulator, and/or read about your state’s regulatory program at the Clearinghouse Web site in the National Summary Citations.