Water Quality Standards are the foundation of the water quality-based pollution control program mandated by the Clean Water Act.
Water Quality Standards define the goals for a waterbody by:
The water quality standards regulation requires that States and authorized
Indian Tribes specify appropriate water uses to be achieved and protected.
Appropriate uses are identified by taking 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.
In designating uses for a water body, States and Tribes examine the suitability
of a water body for the uses based on the physical, chemical, and biological
characteristics of the water body, its geographical setting and scenic qualities,
and economic considerations. Each water body does not necessarily require a unique
set of uses. Instead, the characteristics necessary to support a use can be
identified so that water bodies having those characteristics can be grouped together
as supporting particular uses.
Where water quality standards specify designated uses less than those which are
presently being attained, the State or Tribe is required to revise its standards to
reflect the uses actually being attained. A use attainability analysis must be conducted
for any water body with designated uses that do not include the "fishable/swimmable"
goal uses identified in the §101(a)(2) of the Act. Such water bodies must be reexamined
every three years to determine if new information has become available that would warrant a
revision of the standard. If new information indicates that "fishable/swimmable"
uses can be attained, such uses must be designated.
Water Quality Criteria States and authorized Tribes adopt water quality criteria with
sufficient coverage of parameters and of adequate stringency to protect designated uses.
In adopting criteria, States and Tribes may:
- Adopt the criteria that EPA publishes under §304(a) of the Clean Water Act;
- Modify the §304(a) criteria to reflect site-specific conditions; or
- Adopt criteria based on other scientifically-defensible methods.
States and Tribes typically adopt both numeric and narrative criteria.
Numeric criteria are important where the cause of toxicity is known or for protection against pollutants with
potential human health effects.
Narrative criteria are also important -- narrative "free from" toxicity criteria typically serve as
the basis for limiting the toxicity of waste discharges to aquatic species (based on whole effluent toxicity testing).
§303(c)(2)(B) of the Clean Water Act requires States and authorized Tribes to adopt numeric criteria for
§307(a) priority toxic pollutants for which the Agency has published §304(a) criteria, if the discharge or
presence of the pollutant can reasonably be expected to interfere with designated uses.
The § 307(a) list contains 65 compounds and families of compounds, which the Agency has interpreted to include
126 priority toxic pollutants. In addition to narrative and numeric (chemical-specific) criteria, other types of water
quality criteria include:
- a description of the desired aquatic community, for example, based on the numbers and kinds of organisms
expected to be present in a water body
- a means to protect against nutrient over-enrichment and cultural eutrophication
- a description of conditions that will avoid adverse effects of
contaminated and uncontaminated sediment
Water quality standards include an antidegradation policy and implementation method. The water quality standards regulation
requires States and Tribes to establish a three-tiered antidegradation program.
Tier 1 maintains and protects existing uses and water quality conditions necessary to support such uses. An existing use can
be established by demonstrating that fishing, swimming, or other uses have actually occurred since November 28, 1975, or
that the water quality is suitable to allow such uses to occur. Where an existing use is established, it must be protected
even if it is not listed in the water quality standards as a designated use.
Tier 1 requirements are applicable to all surface waters.
Tier 2 maintains and protects "high quality" waters -- water bodies where existing conditions are better than
necessary to support CWA § 101(a)(2) "fishable/swimmable" uses. Water quality can be lowered in such waters.
However, State and Tribal Tier 2 programs identify procedures that must be followed and questions that must be answered before
a reduction in water quality can be allowed.
In no case may water quality be lowered to a level which would interfere with
existing or designated uses.
Tier 3 maintains and protects water quality in outstanding national resource waters (ONRWs). Except for certain temporary
changes, water quality cannot be lowered in such waters. ONRWs generally include the highest quality waters of the United
States. However, the ONRW classification also offers special protection for waters of exceptional ecological significance,
i.e., those which are important, unique, or sensitive ecologically. Decisions regarding which water bodies qualify to be
ONRWs are made by States and authorized Indian Tribes. Antidegradation implementation procedures identify the steps and
questions that must be addressed when regulated activities are proposed that may affect water quality. The specific steps
to be followed depend upon which tier or tiers of antidegradation apply.
