Protecting Public Health and the Environment.
A water quality standard defines the water quality goals for a water body or portion thereof, in part, by designating the use or uses to be made of the water. The designated beneficial use of a water body must consider its actual use, the ability of the water to support in the future a use that is not currently supported, and the basic goal of the Clean Water Act that all waters support aquatic life and recreation where attainable. Idaho must designate its uses accordingly.
A designated use is a beneficial use assigned to a specific water body in Idaho water quality rules. The Clean Water Act requires Idaho to recognize existing uses, which are uses that are/were actually attained in a water body on or after November 28, 1975, whether or not they are designated uses. Idaho presumes most undesignated waters will support cold water aquatic life and either primary or secondary contact recreation. These are termed presumed uses. Designated, existing, and presumed uses must all be protected.
In designating uses, Idaho takes into consideration the use and value of the water body for public water supply; for protection of fish, shellfish, and wildlife; and for recreational, agricultural, industrial, and navigational purposes. While there may be competing beneficial uses in a river or a stream, federal law requires DEQ to protect the most sensitive of the beneficial uses.
Idaho evaluates the suitability of a water body for the uses based on the following:
In general, different water bodies, and different portions of any given water body, are assigned various combinations of designated uses. A segment will almost always be classified for more than one designated use. The following are the beneficial uses identified in Section 100 of Idaho's Water Quality Standards (IDAPA 58.01.02.100).
The standards associated with this use are designed to protect animal and plant species that live in the water. Some pollutants or conditions that affect aquatic life are water temperature, dissolved oxygen levels, and concentrations of toxic substances such as ammonia, metals, and pesticides. Therefore Idaho's water quality standards set criteria for these pollutants or conditions to protect against adverse effects due to human activities."
The following are subclassifications for the aquatic life designation:
Except for the modified use, the main distinction between the subclassifications of aquatic life is different temperature criteria.
Recreational uses are divided into primary contact and secondary contact recreation. Both of these classifications carry bacteria criteria (IDAPA 58.01.02.251) to protect people from gastrointestinal illness due to incidental ingestion of the water they are recreating in or on. The bacteria levels allowed differ according to the nature of the recreational use and resulting likelihood of unintentionally ingesting water.
Standards associated with this use indicate whether water from a lake or river is suitable for use as a source for a water supply system. Public drinking water is treated before it is delivered to the tap; a separate set of standards governs treated drinking water. Indicators used to measure the safety or usability of surface water bodies as sources for drinking water include turbidity, which may interfere with treatment, and the presence or absence of toxic substances such as metals or pesticides.
The following are subclassifications for the water supply designation:
The standards associated with this use are designed to protect water quality appropriate for wildlife habitat. This use applies to all surface waters of the state.
This use applies to all surface waters of the state.
DEQ determines whether a water body fully supports its designated and existing beneficial uses by evaluating whether the applicable water quality standards and criteria are being achieved and whether a healthy, balanced biological community is present. DEQ's Water Body Assessment Guidance describes a process that uses biological and aquatic habitat parameters, as well as traditional water quality data, to assist in the assessment of beneficial use status.
Bioassessment is particularly useful in judging compliance with Idaho's narrative criteria. The following are bio-assessment parameters that DEQ uses to assess the beneficial use status. These are merely parameters and should not be treated as water quality criteria or applied as water quality standards.
Although numeric water quality are carefully set, it is impossible to pick a single broadly applied value for some measures (e.g., temperature and dissolved oxygen) that is never exceeded naturally, yet is protective of uses. Therefore, Idaho water quality standards allow that if natural background conditions exceed any applicable water quality criteria, there is no impairment of beneficial uses or violation of water quality standards. Natural background conditions alone shall not be the basis for placing a water body on the list of water quality limited water bodies.
Water Quality Standards CoordinatorDon EssigDEQ State Office1410 N. HiltonBoise, ID 83706(208) email@example.com
Water Quality StandardsCommon Water Quality MeasuresNatural Background Conditions