Narrative Water Quality Criteria
To supplement numeric criteria, Idaho has adopted narrative criteria. Such criteria are statements that describe the desired water quality goal, such as Idaho's waters being free from pollutants such as oil and scum, color and odor, and other substances that can harm people and fish. Narrative criteria are statements that guide protection of beneficial uses from impairment by pollutants. Narrative criteria are employed for pollutants for which numeric criteria are difficult to specify, such as color and odor, or where natural occurrence and variability make general limits impractical, such as with sediment and nutrients.
The following narrative water quality criteria apply to all surface waters of the state in addition to the water quality criteria set for specifically designated waters.
Hazardous Materials
Surface waters of the state must be free from hazardous materials in concentrations found to be of public health significance or to impair designated beneficial uses. A hazardous material is one that is harmful to humans and animals due to exposure, but not necessarily ingestion. Hazardous materials include substances that are flammable or corrosive or are strong oxidizing agents. Familiar examples are solvents, such as paint thinners, gasoline, and waste oil, and certain household chemicals such as drain cleaners and pool chemicals.
Toxic Substances
Surface waters of the state must be free from toxic substances in concentrations that impair designated beneficial uses. A toxic substance is a substance that can cause disease, malignancy, genetic mutation, death, or similar consequences. Mercury, dioxin, and most pesticides are toxic substances.
Deleterious Materials
Surface waters of the state must be free from deleterious materials in concentrations that impair designated beneficial uses. Deleterious materials are generally substances that taint edible species of fish, cause taste and odors in drinking water, or cause harm to fish or other aquatic life. Detergents and pharmaceuticals are examples of deleterious materials.
Radioactive Materials
Radioactive materials or radioactivity must not exceed the values or concentrations listed in the Code of Federal Regulations, Title 10, Chapter 1, Part 20.
Floating, Suspended, or Submerged Matter
Surface waters of the state must be free from floating, suspended, or submerged matter of any kind in concentrations causing nuisance or objectionable conditions or in concentrations that may impair designated beneficial uses.
Excess Nutrients
Surface waters of the state shall be free from excess nutrients that can cause visible slime growths or other nuisance aquatic growths that impair designated beneficial uses.
Oxygen-Demanding Materials
Surface waters of the state shall be free from oxygen-demanding materials in concentrations that would result in anaerobic water conditions.
Sediment
Sediment shall not exceed quantities specified in Idaho's water quality standards (IDAPA 58.01.02.250 and .02.252) or, in the absence of specific sediment criteria, quantities that impair designated beneficial uses.
The categories of hazardous; toxic; deleterious; and floating, suspended, or submerged matter do not include suspended sediment produced as a result of nonpoint source activities.