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| 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:
36% of Idaho's homes, or about 210,000 residences, use on-site septic
systems to treat their sewage.
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. |
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| Types of Wastewater Systems |
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Wastewater disposal systems can
generally be divided into two categories: centralized and decentralized.
Centralized systems (different from "central"
systems, discussed below) are public sewer systems (municipal wastewater
treatment plants). These usually serve established towns and cities.
Decentralized systems are smaller, often private, and can be subsurface
disposal systems (on-site systems) or small wastewater treatment
plants. On-site systems are the focus of the discussion below. Read
more about other wastewater treatment systems or view
a graphic showing the types of wastewater systems.
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| On-Site Wastewater Systems |
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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.
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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.
Nutrient-pathogen
(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. Read A
Homeowner's Guide to Septic Systems (pdf 107 kb, 9 pages).
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Large Soil Absorption
Systems |
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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. |
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| Who Regulates 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 Health
Districts under a memorandum
of understanding between DEQ and the Health Districts. The 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 N-P evaluations, when
required. |
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| Installing Septic Systems |
Individual Septic
Systems |
| In order to
have a septic system installed, the property owner must obtain a permit
from the local 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 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 N-P
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 Health District.
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Large Soil Absorption
Systems |
| As
with an individual system, a property owner or developer wishing
to install an LSAS must obtain a permit from the local 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 specification review by DEQ. The 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 N-P
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 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. Read A
Guide to Community Septic Systems (pdf 249 kb, 11 pages).
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| For More Information |
| Individual/Subsurface
Sewage Disposal Rules (IDAPA 58.01.03) (pdf
on Department of Administration Web page) |
| Nutrient-Pathogen Evaluations
|
| Septic
Systems Reports and Guidance |
| Wastewater
Systems |
