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Water Quality Criteria
[Why
are WQS Important?] [WQS
Review and Revision] [Role
of the Public] [Designated
Uses] [Water
Quality Criteria] [Antidegradation]
[General Policies]
[Indian Tribe Participation]
[WQS Program History]
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).
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:
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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
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nutrient
criteria: a means to protect against nutrient
over-enrichment and cultural eutrophication
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sediment criteria: a description of conditions
that will avoid adverse effects of contaminated
and uncontaminated sediments
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