Septic systems are used to treat and dispose of relatively small volumes of wastewater, usually from houses and businesses that are located relatively close together. Septic systems are also called onsite wastewater treatment systems, decentralized wastewater treatment systems, on-lot systems, individual sewage disposal systems, cluster systems, package plants, and private sewage systems. Because septic systems do not involve central wastewater collection and treatment, they are considered decentralized.

How do septic systems work?

The typical septic treatment system includes a septic tank, which digests organic matter and separates floatable matter (e.g., oils and grease) and settleable solids from the wastewater. Soil-based systems discharge the liquid (effluent) from the septic tank into a series of perforated pipes buried in a leach field, leaching chambers, or other special units designed to slowly release the effluent into the soil or surface water.

Alternative systems use pumps or gravity to help septic tank effluent trickle through sand, organic matter (e.g., peat, sawdust), constructed wetlands, or other media to remove or neutralize pollutants like disease-causing pathogens, nitrogen, phosphorus, and other contaminants. Some alternative systems are designed to evaporate wastewater or disinfect it beefore it is discharged to the soil or surface waters.

Do septic systems cause health or water quality problems?

Septic systems that are properly planned, designed, sited, installed, operated and maintained can provide excellent wastewater treatment. However, systems that are sited in densities that exceed the treatment capacity of regional soils and systems that are poorly designed, installed, operated or maintained can cause problems. The most serious documented problems involve contamination of surface waters and ground water with disease-causing pathogens and nitrates. Other problems include excessive nitrogen discharges to sensitive coastal waters and phosphorus pollution of inland surface waters, which increases algal growth and lowers dissolved oxygen levels. Contamination of important shellfish beds and swimming beaches by pathogens is also a concern in some coastal regions. EPA has developed Guidelines to assist communities in establishing comprehensive management programs for septic wastewater systems to improve water quality and protect public health.

How are septic systems regulated?

In most states, local health departments issue construction and operating permits to install septic systems under state laws that govern public health protection and abatement of public nuisances. Some states are beginning to add water resource protection provisions to their septic system regulations because of the possible impacts from nitrogen and phosphorus. Under most regulatory programs, the local permitting agency conducts a site assessment to determine whether the soils present can provide adequate treatment, to ensure that ground water resources will not be threatened, and to stipulate appropriate setback distances from buildings, driveways, property lines and surface waters. Some states permit alternative systems if conventional soil-based systems are not allowable. Very few permitting agencies conduct regular inspections of septic systems after they are installed.

Source: EPA