Water Quality Standards

What Are They?

Water Quality Standards are the foundation of the water quality-based control program mandated by the US EPA Clean Water Act.

Water Quality Standards define the goals for a waterbody by designating its uses, setting criteria to protect those uses, and establishing provisions to protect water quality from pollutants.

Four Basic Elements Of Water Quality Standards

1. Designated Uses of the water body (e.g., recreation, water supply, aquatic life, agriculture),

2. Water Quality Criteria to protect designated uses (numeric pollutant concentrations and narrative requirements),

3. An Antidegradation Policy to maintain and protect existing uses and high quality waters, and

4. General Policies addressing implementation issues (e.g., low flows, variances, mixing zones).

Water Quality Map By Region

Which region do you live in on the Water Quality Standards Map

Water Quality Standards - Designated Uses

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.

Water Quality Standards - 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).

Section 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:

Biological Criteria: 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.

Nutrient Criteria: a means to protect against nutrient over-enrichment and cultural eutrophication.

Sediment Criteria: a description of conditions that will avoid adverse effects of contaminated and uncontaminated sediments.

Water Quality Standards - Antidegradation Policy

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 Water Quality Standards

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 Water Quality Standards

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 Water Quality Standards

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.

Water Quality Standards - General Policies

States and Tribes may adopt policies and provisions regarding water quality standards implementation, such as mixing zone, variance, and low-flow policies. Such policies are subject to EPA review and approval.

Mixing Zones: States and Tribes may, at their discretion, allow mixing zones for point source discharges.

A mixing zone is a defined area surrounding or downstream of a point source discharge where the effluent plume is progressively diluted by the receiving water and numeric criteria otherwise applicable to the segment may be exceeded.

Mixing zone procedures describe the methodology for determining the location, size, shape, and in-zone quality of mixing zones.

Variances: As an alternative to removing a designated use, a State or Tribe may wish to include a variance as part of a water quality standard. Variances temporarily relax a water quality standard.

They are subject to public review every three years, and may be extended upon expiration. A variance may specify an interim water quality criterion which is applicable for the duration of the variance. Variances can help to assure that further progress toward improving water quality is achieved.

Low Flows: State and Tribal water quality standards may identify policies and procedures to be applied in determining critical low flow conditions. Such procedures are applied, for example, when calculating discharge permit requirements to be included in National Pollutant Discharge Elimination System (NPDES) permits.

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