Protecting Public Health and the Environment.

Extended Treatment Package Systems (Aerobic Treatment Units)

Extended treatment package systems (ETPSs) are manufactured and packaged mechanical treatment devices that provide biological treatment to septic tank effluent before the effluent’s discharge to a drainfield. ETPSs are also commonly referred to as aerobic treatment units. The biological treatment provided by ETPSs is done under aerobic conditions that facilitate the growth of aerobic bacteria. The aerobic conditions and bacterial growth are made possible by extended aeration, contact stabilization, rotating biological contact, trickling filters, attached growth media, other approved methods, or combination of any of these methods. The enhanced treatment provided by ETPSs occurs after primary clarification of wastewater in an appropriately sized septic tank.

Enhanced Treatment

Enhanced treatment of septic tank effluent through use of an ETPS may be required for certain parcels based on certain site features such as, but not limited to, the following:

  • Shallow soil depths
  • Predominance of coarse- or very coarse-grained soils
  • Shallow ground water depth
  • Outcome of a nutrient-pathogen evaluation

ETPSs are capable of providing an 85% reduction or better in total suspended solids (TSS) and carbonaceous biological oxygen demand (CBOD5) in septic tank effluent. Additionally, some ETPSs are also capable of providing a reduction of total nitrogen (TN) in septic tank effluent. These improvements in effluent quality are necessary to protect sensitive environmental areas and  the function of the drainfield. To ensure an ETPS unit is capable of providing enhanced treatment to septic tank effluent, specific operation and maintenance procedures must be performed.

Operation, Maintenance, and Monitoring

Operation and maintenance procedures for ETPS units vary among the manufacturers. Each manufacturer has specific operation and maintenance procedures that need to be followed. As part of the septic permit issued for an ETPS unit, Idaho requires that a minimum of one operation and maintenance event occurs for each ETPS unit annually. This requirement is allowed by DEQ’s Individual/Subsurface Sewage Disposal Rules (IDAPA 58.01.03) as a condition of issuing a subsurface sewage disposal permit (septic permit) (IDAPA To ensure the effluent discharged from an ETPS unit is meeting the required reduction levels, annual monitoring is also required.

Monitoring refers to the testing of effluent quality discharged from an ETPS unit. Monitoring is also a requirement allowed by IDAPA 58.01.03 as a condition of issuing a septic permit. Monitoring is required annually and is typically performed after annual operation and maintenance is performed on an ETPS unit. Effluent samples are submitted to a laboratory capable of meeting the effluent analysis standards for ETPSs specified in the Technical Guidance Manual for Individual and Subsurface Disposal Systems (TGM). Effluent is analyzed for concentrations of TSS, CBOD5, and if required TN. All ETPS units must produce effluent meeting the quality standards of 45 milligrams per liter (mg/L) (parts per million [ppm]) TSS and 40 mg/L (ppm) CBOD5. Effluent standards for TN are specific to each septic permit issued with TN reduction requirements. If any of the effluent samples fail to meet the minimum quality standards, then additional ETPS maintenance and monitoring are required to be performed until the effluent quality meets the minimum septic permit requirements. Operation, maintenance, and monitoring are required to be performed by a service provider that works for an approved operation and maintenance (O&M) entity.

Operation and Maintenance Entities

To obtain a septic permit for a septic system with an ETPS unit an applicant must submit a member agreement with an O&M entity capable of providing operation, maintenance, and monitoring services related to the ETPS unit. O&M entities that have documented they are capable of meeting the minimum operation, maintenance, and monitoring services for ETPS units are listed in DEQ’s nonprofit O&M list for ETPSs. The member agreement for these O&M entities is a document that provides the following:

  • Outline of the services that the O&M entity will provide the property owner.
  • Access easement agreement between the property owner and O&M entity.
  • Description of the dues the property owner must pay annually to the O&M entity.

The member agreement is signed by both the property owner and O&M entity representative and is recorded in the county that the property is located within. Member agreements are required to be submitted to a public health district as part of the septic permit application as allowed by IDAPA,, and before a septic permit is issued. This ensures that the property owner has a means of performing the required annual operation, maintenance, and monitoring for their ETPS unit.

O&M entities are nonprofit corporations created specifically to provide continual operation, maintenance, and monitoring services for their member’s ETPS units. Members of an O&M entity are afforded voting rights over certain aspects of their O&M entity’s operations as allowed through the individual O&M entity’s articles of incorporation and bylaws. Every member should maintain a copy of their O&M entity’s articles of incorporation and bylaws. The O&M entity contracts with service providers to perform the required operation, maintenance, and monitoring services for their members. The number of service providers an O&M entity contracts to provide these services depends on the O&M entity’s needs. Service providers should be provided with manufacturer-approved training for the ETPS units that they service. Any issues an O&M entity member has with the service provider should be addressed with the O&M entity.

Although a property owner (member) is contracted with an O&M entity to perform the annual operation, maintenance, and monitoring, it is the member’s responsibility to ensure the requirements of the septic permit are met on an annual basis. The property owner’s responsibilities are defined in the IDAPA These responsibilities include not only that the operation, maintenance, and monitoring are performed but also that these activities are reported to the septic permit-issuing public health district on an annual basis.

Annual Reporting

To ensure that a member is fulfilling the operation, maintenance, and monitoring requirements associated with their ETPS unit and septic permit, the member is responsible for submitting an annual report to the public health district that issued their septic permit. The annual report documents all of the operation and maintenance activities that occurred during the reporting year for the property owner’s ETPS unit. Additionally, the annual report contains all of the laboratory analysis results related to the effluent sampling for the property owner’s ETPS unit. This annual report may either be submitted by the property owner or their contracted O&M entity, but the responsibility of ensuring the annual reporting requirements are fulfilled lies with the property owner. Annual reports are required to be submitted to the public health district that an ETPS unit is located within by June 30 every year.

Additional Information

An in-depth description of ETPS operation, maintenance, monitoring, and annual reporting requirements is found in the Extended Treatment Package System section of the TGM. Additional information is also available in DEQ’s Resource links located on the right-hand sidebar of this web page. Property owners are encouraged to educate themselves regarding ETPS units and their associated septic permit requirements before installing one.

ETPS units must have a constant supply of electricity to function property. Shutting off the power supply to any of an ETPS unit’s electrical components will compromise the unit’s function and will result in additional operation, maintenance, and monitoring costs for the property owner. The savings in an electrical bill by shutting off an ETPS unit’s power supply will be greatly outweighed in the additional operation, maintenance, and monitoring costs. Property owners should contact their O&M entity before altering an ETPS unit or any of the unit’s associated components.

Aerobic bacterial growth within an ETPS unit is vital to the unit’s function. Bacteria are living organisms and are sensitive to their environment. Any products that a property owner puts down the drain will impact the function of their ETPS unit. Care should be taken not to overload a septic system with household cleaning products (chemicals), unconsumed medicine, or trash. Household cleaning products poured down a drain or placed in a toilet should be limited and diluted. Unconsumed medicine should be destroyed and disposed of in the garbage. Any nontoilet paper-related trash should also be disposed of in the garbage. Garbage disposals also impact the function of ETPS units and their use should be extremely limited. Kitchen sinks should be strained and all byproducts should be disposed of in the garbage. Property owners should contact their O&M entity regarding household water use practices to ensure the best possible function of their ETPS unit.

Septic tanks require pumping on a semiregular basis (every 3–5 years) to remove the fats, oil, grease, and settled solids from the tank. ETPS units may also require more frequent periodic pumping. Any pumping of the ETPS unit should occur under the direction of a property owner’s service provider. The service provider’s supervision will help to ensure that the ETPS unit continues to function properly and may prevent any damage to the unit from the pumping process. Service providers should inform the property owner of the need to pump the ETPS unit. Property owners should not allow a permitted pumper to pump their ETPS unit without approval from their O&M entity or service provider.