On-Site Wastewater Systems (Septic Systems)

Many homes and other buildings that are not served by public sewer systems depend on "on-site"septic systems to treat and dispose of wastewater. On-site systems use a septic tank andunderground (subsurface) drainfield to treat wastewater on-site. On-site systems are the mostcommon wastewater treatment system used in rural areas of Idaho.

Septic systems dispose of household sewage, or wastewater, generated from toilet use, bathing,laundry, and kitchen and cleaning activities. A system that is not functioning properly will releasenutrient-rich and bacteria-laden wastewater into the ground water and/or surface water. A properlydesigned, located, constructed, and maintained septic system is imperative to protecting humanhealth and the environment.

Regulation of Septic Systems in Idaho

DEQ has established minimum standards, the Individual/Subsurface Sewage Disposal Rules, for thedesign, construction, siting, and use of individual and subsurface sewage disposal systems. This rulealso establishes requirements for obtaining an installation permit and an installer's registrationpermit.

These rules are administered by Idaho's seven local Public Health Districts under a memorandum ofunderstanding between DEQ and the Public Health Districts. ThePublic Health Districts permitand inspect septic systems, and, for a fee, also conduct site evaluations to determine the suitabilityof a location for a septic system. DEQ conducts plan and specification review for central and largesoil absorption systems and reviews Nutrient-Pathogen (NP) evaluations, which are scientificevaluations of the water quality impacts of septic systems, when required.

Types of Septic Systems

On-site wastewater systems discharge wastewater into an underground tank where solids and waterare separated. Solids settle to the bottom of the tank. Bacteria in the tank break down organicmatter. Water (effluent) flows from the tank and into a drainfield of underground pipes surroundedby gravel and soil. The pipes slowly release the water and the gravel and soil filter out remainingcontaminants before the water reaches the ground water. Residual sludge in the tanks must bepumped out periodically.

Individual Septic Systems

An individual septic system is a decentralized system that serves one or two homes and usuallyconsists of a 1,000-gallon concrete septic tank and a drainfield or leach field. N-P evaluations may berequired for individual septic systems in new subdivisions. Some individual systems may be"enhanced" to provide extra filtration or treatment between the septic tank and the drainfield.

In order to have a septic system installed, the property owner must obtain a permit from thelocal Public Health District. The permit states the conditions and requirements necessary for theseptic system. It is recommended that the property owner have a site evaluation performed by theHealth District and a licensed septic system installer before applying for a permit and before

purchasing property. Not all property is suitable for septic systems, so some permits may be denied.Depending on the location of the property and the type of system being installed, an NP evaluationmay be required as part of the permit application. Once the permit has been issued, the systemshould be installed by a licensed installer and inspected by the local Public Health District.

Large Soil Absorption Systems

A large soil absorption system (LSAS) is a subsurface sewage disposal system designed to receive2,500 gallons per day or more. Developments and facilities such as resorts, schools, subdivisions,and rest areas that are not connected to centralized systems often use LSASs to treat theirwastewater. A LSAS is one type of central system, which is any system that receives wastewaterfrom two or more homes or buildings or receives more than 2,500 gallons per day of wastewater.

As with an individual system, a property owner or developer wishing to install an LSAS must obtaina permit from the local Public Health District. In addition, the LSAS design must be prepared by aprofessional engineer licensed by the state of Idaho and must undergo plan andhttp://utilities.emporia-kansas.gov/index.php/water-treatment-plant specification review by DEQ. ThePublic Health Districts provide the plans to DEQ for review and issue the LSAS permit after DEQ hascompleted the review and has issued a letter approving the system for construction. DEQ requiresan NP evaluation as part of the permit application for all LSASs. Prior to issuing a permit, HealthDistrict staff will conduct an on-site evaluation and inspect test holes on the property in the area ofthe proposed drainfield.

Large soil absorption systems must be installed by a licensed complex installer and inspected by theHealthhttp://www.pbslearningmedia.org/resource/ess05.sci.ess.watcyc.h2otreatment/water-treatment-plant/ District and DEQ. An annual operation and maintenance report must be sent to DEQ and theHealth District each year. Some permits may also require monthly ground water monitoring.

Nutrient-Pathogen Evaluations

Septic systems have the potential to transport pollutants from sewage to ground water. To helpprevent this, nutrient-pathogen evaluations are required for certain proposed on-site wastewaterdisposal systems. The evaluations consist of scientific analyses of potential water quality impacts ofon-site subsurface sewage disposal systems. Learn more.

Technical Guidance Manual

The Technical Guidance Manual for Individual and Subsurface Sewage Disposal Systems providesguidance on the design, construction, alteration, repair, operation and maintenance of standardindividual and subsurface sewage systems, their components, and alternatives. Access the manualand information on activities of the Technical Guidance Committee here.

Extended Treatment Package Systems

Extended treatment package systems (ETPSs) are manufactured and packaged mechanicaltreatment devices that provide biological treatment to septic tank effluent prior to the effluent'sdischarge to a drainfield. ETPSs are also commonly referred to as aerobic treatment units. Learnmore.

https://www.deq.idaho.gov/water-quality/wastewater/septic-systems.aspx