Septic Systems Overview
More than one in five households in the United States depend on an individual onsite system or small community cluster system to treat their wastewater. These systems are used to treat and dispose of relatively small volumes of wastewater, usually from houses and businesses that are located relatively close together.
Onsite wastewater systems include a wide range of individual and cluster treatment systems that process household and commercial sewage.
Onsite systems are also called:
- septic systems,
- decentralized wastewater treatment systems,
- cluster systems,
- package plants,
- on-lot systems,
- individual sewage disposal systems, and
- private sewage systems.
The various types of decentralized wastewater treatment, if properly executed, can protect public health, preserve valuable water resources, and maintain economic vitality in a community. They are a cost-effective and long-term option for treating wastewater, particularly in less densely populated areas.
What are the benefits of using septic systems to manage wastewater from small communities?
- Public health benefits - Proper use of decentralized systems reduces the risk of disease transmission and human exposure to pathogens, which can occur through drinking water, surface water, and shellfish bed contamination.
- Environmental benefits - Wastewater treatment removes pollution from surface water, recharges groundwater, and replenishes aquifers.
- Economic benefits - Decentralized wastewater systems help communities reduce large infrastructure and energy costs to collect and treat wastewater.
Are septic systems more prevalent in some areas of the country?
The U.S. Bureau of the Census reports that the distribution and density of septic systems vary widely by region and state, from a high of about 55 percent in Vermont to a low of about 10 percent in California.
- New England states have the highest proportion of homes served by septic systems. New Hampshire and Maine both report that about one-half of all homes are served by individual systems.
- More than one-third of the homes in the southeastern states depend on these systems, including approximately 48 percent in North Carolina and about 40 percent in both Kentucky and South Carolina.
- More than 60 million people in the nation are served by septic systems. About one-third of all new development is served by septic or other decentralized treatment systems.
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 a concern in some coastal regions.
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 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 can provide adequate treatment. These programs ensure that ground water resources will not be threatened, and 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.
Regulation of onsite wastewater treatment systems:
- Individual onsite systems are regulated by states, tribes and local governments.
- Large capacity septic systems are regulated under EPA’s Safe Drinking Water Act Underground Injection Well program, large capacity septic systems requirements.
- Systems discharging to surface waters are regulated under EPA’s Clean Water Act National Pollutant Discharge Elimination System program.
- Disposal of sewage sludge (biosolids) and domestic septage are regulated under EPA’s sewage sludge regulation (PDF) (1 pg, 107 K, About PDF) (40 CFR Part 503).
- A Guide to the Biosolids Risk Assessment for the EPA Part 503 Rule describes the risk assessment process that is the basis for the biosolids rule.
What terms are commonly used when talking about Septic Systems?
EPA’s Glossary of Septic System Terminology contains terms commonly used in the wastewater treatment field and their definitions.