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Underground Injection Control (UIC)

Large-Capacity Septic Systems

This page will explain how large-capacity septic systems (LCSSs) are defined, how and why LCSSs are regulated, and where to find additional information.

What is a septic system?
What is a large-capacity septic system?
What is not a large-capacity septic system?
Why does EPA regulate large-capacity septic systems?
What are the minimum federal requirements for large-capacity septic systems?
How is EPA helping to improve the performance of large-capacity septic systems?
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What is a septic system?

A septic system is an on-site method of treating and disposing of sanitary wastewater. A typical septic system often consists of the following:

  • Buried tank - removes suspended solids from raw wastewater
  • Effluent distribution system 
  • Soil absorption area – provides for additional effluent treatment and attenuation through the processes of adsorption, dispersion, and biodegradation

Septic systems may also have grease traps or other pre-treatment technologies.  More sophisticated designs can include several small septic tanks that drain to a dry well, or connections to multiple absorption areas used on a rotating basis.

Septic systems are commonly found in rural and suburban areas where people often rely on ground water for their drinking water. Septic systems that are properly sited, designed, constructed, operated, and maintained pose little threat to drinking water sources. However, poorly designed, maintained, or operated septic systems can contaminate ground water or surface water. 

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What is a large-capacity septic system?

A septic system is considered a large capacity septic system (LCSS) if it receives solely sanitary waste either from multiple dwellings or from a non-residential establishment and the system has the capacity to serve 20 or more persons per day.

In general, LCSSs may be found serving the following facilities:

  • Apartment buildings
  • Trailer parks
  • Schools and religious institutions
  • Office, industrial, and commercial buildings
  • Shopping malls
  • State parks and campgrounds
  • Recreation or vehicle (RV) parks
  • Highway rest areas
  • Train and bus stations
  • Hotels and restaurants
  • Casinos

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What is not a large-capacity septic system?

Once a large capacity septic system (LCSS) is used to inject anything other than sanitary waste it is no longer an LCSS.  For example, the disposal of industrial waste into an LCSS for example makes it an industrial waste water disposal well. Similarly, a septic system that receives vehicular repair or maintenance waste is known as a motor vehicle waste disposal well. Toxic chemicals can pass through these systems untreated, enter the ground water and possibly endanger USDWs.

To safeguard against this type of contamination, the Safe Drinking Water Act (SDWA) requires that EPA set minimum federal requirements to prevent the endangerment of underground sources of drinking water. 

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Why does EPA regulate large-capacity septic systems?

The SDWA directs EPA to establish minimum federal requirements for state and tribal Underground Injection Control (UIC) programs to protect underground sources of drinking water (USDWs) from contamination caused by injection activities (such as placing or discharging waste fluids underground). Protective requirements include the oversight of construction, operation, and closure of injection wells.

The UIC program is designed to protect USDWs and provide safe and cost-effective means for industries, municipalities, and small businesses to dispose of their wastewater, extract mineral resources, and store water for the future. Illegal discharges have the potential to contaminate our drinking water resources. Preventing contamination of these resources protects the public and the economic health of communities nationwide.

States and tribes may apply to EPA for authority to administer the UIC program. States and tribes that receive such authority must meet the minimum federal requirements; however, state and tribes can always adopt more stringent requirements.

The UIC program regulates the shallow injection of non-hazardous fluids in a category called Class V wells. An LCSS is considered a type of Class V well. 

EPA does not regulate septic systems used by single-family homes or non-residential septic systems receiving solely sanitary waste that serve fewer than 20 persons per day. However, if these systems are improperly sited, operated or maintained they can threaten water quality. EPA has the authority to address malfunctioning systems on a case-by-case basis. States and local authorities may also have their own requirements to address these threats. 

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The majority of Class V wells, including LCSSs, are "authorized by rule" provided they meet these minimum federal requirements:

  • The owner or operator must submit basic inventory information to the permitting authority
  • The injectate cannot endanger USDWs

"Authorized by rule" means that an individual permit is not required. Local, state, or tribal rules governing these wells may be more stringent than the federal regulations. To determine the LCSS requirements in your state, check with your permitting authority. Inventory information includes:

  • Facility name and location
  • Owner's or operator's name and address 
  • Nature and type of injection well
  • Operating status

The second minimum federal requirement prohibits injection that allows the movement of fluids containing any contaminants (such as pathogens, solvents, or heavy metals) into a USDW if the presence of that contaminant may cause a violation of any primary drinking water regulation or adversely affect public health.

The potential for contaminants to endanger USDWs depends on a variety of site-specific factors such as:

  • Soil
  • Hydrogeology
  • Wastewater characteristics
  • System design

Soil is an integral part of the design for an LCSS receiving solely sanitary waste and should be a fundamental to designing an effective system. Attenuation occurs as the septic tank effluent travels through the soil below the drain field. Dissolved organic matter, pathogens, and some inorganic constituents can be attenuated in unsaturated soils below the drain field.

If the LCSS is designed, operated, and maintained properly, it generally should not endanger USDWs. To find out who makes these decisions in your state, contact either the state or local health department or UIC permitting authority.

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EPA is working with state and local health departments to ensure that the minimum federal requirements for Class V wells are met before an LCSS is permitted. In addition to educating owners and operators, EPA has a wide variety of tools and resources to assist state and local governments in improving the management and performance of septic systems.

The cooperative relationship between EPA, states, and communities can ensure that all LCSSs are managed and regulated at the local level consistently in a manner that protects drinking water sources.

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