On-site wastewater systems, or septic systems, are crucial for treating and disposing of wastewater in rural areas of Idaho where public sewer systems are unavailable. The Idaho Department of Environmental Quality (DEQ) has set regulations for the design and operation of these systems, including permitting and inspections by local public health districts. Both individual septic systems and large soil absorption systems require proper installation and periodic maintenance to prevent environmental contamination.

1. 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 and
underground (subsurface) drainfield to treat wastewater on-site. On-site systems are the most
common 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 release
nutrient-rich and bacteria-laden wastewater into the ground water and/or surface water. A properly
designed, located, constructed, and maintained septic system is imperative to protecting human
health and the environment.
Regulation of Septic Systems in Idaho
DEQ has established minimum standards, the Individual/Subsurface Sewage Disposal Rules, for the
design, construction, siting, and use of individual and subsurface sewage disposal systems. This rule
also establishes requirements for obtaining an installation permit and an installer's registration
permit.
These rules are administered by Idaho's seven local Public Health Districts under a memorandum of
understanding between DEQ and the Public Health Districts. ThePublic Health Districts permit
and inspect septic systems, and, for a fee, also conduct site evaluations to determine the suitability
of a location for a septic system. DEQ conducts plan and specification review for central and large
soil absorption systems and reviews Nutrient-Pathogen (NP) evaluations, which are scientific
evaluations 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 water
are separated. Solids settle to the bottom of the tank. Bacteria in the tank break down organic
matter. Water (effluent) flows from the tank and into a drainfield of underground pipes surrounded
by gravel and soil. The pipes slowly release the water and the gravel and soil filter out remaining
contaminants before the water reaches the ground water. Residual sludge in the tanks must be
pumped out periodically.
Individual Septic Systems
An individual septic system is a decentralized system that serves one or two homes and usually
consists of a 1,000-gallon concrete septic tank and a drainfield or leach field. N-P evaluations may be
required 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 the
local Public Health District. The permit states the conditions and requirements necessary for the
septic system. It is recommended that the property owner have a site evaluation performed by the
Health District and a licensed septic system installer before applying for a permit and before

2. 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 evaluation
may be required as part of the permit application. Once the permit has been issued, the system
should 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 receive
2,500 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 their
wastewater. A LSAS is one type of central system, which is any system that receives wastewater
from 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 obtain
a permit from the local Public Health District. In addition, the LSAS design must be prepared by a
professional engineer licensed by the state of Idaho and must undergo plan and
http://utilities.emporia-kansas.gov/index.php/water-treatment-plant specification review by DEQ. The
Public Health Districts provide the plans to DEQ for review and issue the LSAS permit after DEQ has
completed the review and has issued a letter approving the system for construction. DEQ requires
an NP evaluation as part of the permit application for all LSASs. Prior to issuing a permit, Health
District staff will conduct an on-site evaluation and inspect test holes on the property in the area of
the proposed drainfield.
Large soil absorption systems must be installed by a licensed complex installer and inspected by the
Health
http://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 the
Health 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 help
prevent this, nutrient-pathogen evaluations are required for certain proposed on-site wastewater
disposal systems. The evaluations consist of scientific analyses of potential water quality impacts of
on-site subsurface sewage disposal systems. Learn more.
Technical Guidance Manual
The Technical Guidance Manual for Individual and Subsurface Sewage Disposal Systems provides
guidance on the design, construction, alteration, repair, operation and maintenance of standard
individual and subsurface sewage systems, their components, and alternatives. Access the manual
and information on activities of the Technical Guidance Committee here.
Extended Treatment Package Systems
Extended treatment package systems (ETPSs) are manufactured and packaged mechanical
treatment devices that provide biological treatment to septic tank effluent prior to the effluent's
discharge to a drainfield. ETPSs are also commonly referred to as aerobic treatment units. Learn
more.

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